How to add a repair material for 2021.1 (1.12.2) through code?

I am currently making a mod for 1.12.2 on 2021.1 since it is the only version that supports it. I've added some armor, however it has been confirmed in this post https://mcreator.net/tracker/issue/56070 that you are unable to add a repair material. You are able to edit the code of armor though, I just don't know how to add a repair material through the code.

It would be amazing if someone could help me solve this, thanks.