Hello, I am currently trying to create an artificier homebrew spell that adds your intelligence modifier to the total damage amount. Does anybody here know how to do so? 

For more context I'm using firebolt as a template, does that have anything to do with how you add it, or do you need to create it from scratch?

Thanks.

if you go to the damage modifeir you can specify an ability score in this case int and it will add it to the damage 

I don't see any ability score option after selecting the damage modifier?

Thanks.

their should be a checkbox that says use primary stat that adds the spellcasting ability to the effect check off this box