So my DM is giving me a new weapon as a cleric that will partially function like the Moon Sickle with the bonus d4 when using a healing spell, but I can't figure out how to use it. Does anybody have a guide, a link, or instructions on how I do this?

The easiest way to figure it out is to use the Moon Sickle as a template for your magic item and then gust change it from a sickle to a whatever.

(But I’ll do you a favor and let you know that 1d4! Is just txt in a description and it has to be remembered by the player and rolled separately.)

Testing the official Moon Sickle also doesn't the d4 unfortunately. There is a homebrew modifier for adding a dice to the 'healing spell group' however it doesn't seem to work with Healing Word.

The modifier doesn’t work for homebrew, only official stuff.

Ah ok the Bonus - Spell Group - Healing 1d4 didn't work. But also the official Moon Sickle also doesn't work.

The system isn’t smart enough to combine die rolls like that. That modifier works with a fixed value (instead of a die roll) on the Life Domain Cleric’s feature.

 What's strange is the bonus dice is there in the options.

Those forms are designed to be one size fits all, so the option is there, but not all options work with all Modifiers. Please see the General Homebrew FAQ #s 1-3 for more information: (https://www.dndbeyond.com/forums/dungeons-dragons-discussion/homebrew-house-rules/131411-a-homebrewers-how-to-faq).