IM currently trying to make a playable golem race (not as op as it sounds, you'll see if I choose to release it) and I'm trying to make it have subraces based on what it is made of, like ice or clay, and i want those subraces to have different innate spellcasting ability's. I know tiefling subraces have different spellcasting but I can't use those as a template for my race to see how the modifiers in the page work. Any help?

You can use those Tiefling sibraces as templates just to see how they work and not actually use them as templates for your race but simply delete them. Basically dissect them like the worm in biology class and then throw them away. (That is if you have access to them.)

Regardless, where you attach the Spells to your Subrace is where you would designate their spellcasting ability on a spell-by-spell basis:

That is if you have access to them

I don't, i only have access to most of the content through shared content, so ic ant use any of that content in the homebrew builder or things (i tried to do it once already, i wanted to make a reworked circle of stars druid circle and i couldn't use it as a base)

You can use the standard Tiefling as a template as it is free content.

I believe the Tieflings are variants rather than sub-races; you want to use sub-races when you have a core class that isn't intended to be played on its own (in the same way that we don't play as an Elf, but instead as a High Elf, Wood Elf etc.). Variants however are designed to override traits from the parent race, this is what allows variant Tieflings to provide their own replacement to Infernal Legacy as you'll have the option for a trait to either be new, or a replacement.

It sounds like what you probably want is to create a parent golem race with sub-races; don't provide the parent with any spellcasting feature. Then for each sub-race, add the appropriate spellcasting feature for that type of golem. This way the parent golem defines the basic attributes common to all golems, and the sub-races add the specifics for each type.

However, personally I've stopped using sub-races for D&D Beyond as they're a pain to maintain if you need to change the parent race at all (as you need to re-create every sub-race, and end up with multiple cluttering up your homebrew creations). I now prefer to use options to model sub-races, as that way you can edit everything from a single race and I find it a lot easier overall; I've tried to write a guide about how to do this.

Where it can get complicated is if you want to provide spellcasting with a choice of spellcasting abilities (Intelligence, Wisdom or Charisma) as most new races now do; the D&D Beyond homebrew doesn't give us a simple way to do that, meaning you need a separate option for each spellcasting ability, with each granting the appropriate spells set to use that ability score.

If all golems will have spellcasting though you can still keep this reasonably simple by having one trait where you choose the type of golem, then a second spellcasting trait with options tied to each type of golem (so you only see the ones appropriate to that type).

For example, literally yesterday I decided that the current Tiefling and variants is too inflexible for my group, as Tieflings are popular but we don't like being tied to Charisma, or having only the spell options presented. So I took all the variants and boiled them down into an options-based "Custom Tiefling". This has an option to choose either Hellish Resistance (fire damage) or Icy Resistance (cold damage), then under Infernal Legacy there are options for Hellish Magic (Intelligence), Hellish Magic (Wisdom) and so-on offering the spell choices that correspond to each type, so the Hellish Magic options have Hellish Resistance as a prerequisite, so a Tiefling with Icy Resistance won't see them. Since I doubt I can release the homebrew on D&D Beyond (and it's replicating official content) here's what that the details page for that looks like.

Unfortunately that means a lot of replication (each option needs three spell entries for the cantrip and two spells granted at 1st-, 3rd- and 5th-level) and if you have more than two base types you'll need 12 options in total, but that's true using sub-races as well, the options would just be split across them.

One question that may be worth asking is, how important is it that each type is totally distinct? Sometimes it may be better to just players options and let them build whatever they want from those options, then decide for themselves that it's "clay" golem rather than a "rock" golem or whatever? You can still specify the types, or even give recommend builds, as flavour text to inform players, but otherwise make it more like a toolkit.

For the Tiefling example above this is what I opted for, rather than trying to reproduce the various specific spell options for each Tiefling variant, and this made it a lot easier to implement. If you went for this style, you might not need spellcasting options for each type of golem, you could offer a choice of basic features, then just have spellcasting with a set of different spells to choose from, organised under just three options (one per spellcasting ability)?

Sorry if all this seems complicated; but sadly D&D Beyond homebrew can be, as sub-races can be a pain in the ass in homebrew, and we don't have a way to override spellcasting ability (so it has to be multiple redundant options at the moment).