specifically, creatures from the 9 Hells. I just joined a homebrew campaign and the world is filled with creatures from the 9 hells.

I'm a 6th level Wizard, so I have cantrips and spells up to 3rd level. TIA!

Is there some reason you cannot just look at the spells yourself? 

Here are the spells from Basic Rules for Wizards for cantrips up to 3rd level: https://www.dndbeyond.com/spells/class/wizard?filter-search=&filter-level=0&filter-level=1&filter-level=2&filter-level=3&filter-verbal=&filter-somatic=&filter-material=&filter-concentration=&filter-ritual=&filter-sub-class=&filter-source=1&filter-partnered-content=f

You can check spells by going Game Rules >> Spells and filtering as needed. This will solve any and all "what spell is best" questions you may have. 

As for spells specifically for planar creatures, there's not many. 

Protection From Evil and Good
Magic Circle

Generally you deal with planar creatures the same you would any other creature. Buffs on you and party, debuffs and damage to enemy. That will be the tactic for pretty much nearly all enemies in D&D.

I am in the process of reviewing all of the cantrips and level 1-3 Wizard spells. And in order to determine if these spells will be effective against creatures from the 9 hells, I'm also reviewing fiends in the monster search on here. There are lot of spells and there are over 50 fiends under CR 10. That's a lot of info to digest, but I'm slogging through it. I'm trying to figure out if there are certain common resistances and/or immunities that creatures from the 9 hells have that would determine which spells to prepare. I didn't think there was a problem with reviewing the spells myself and asking others about their experience casting against creatures from the 9 hells.