Custom Module - Module Builder - Index Field for import dedup?

Hey team,

How do you go about setting fields as index fields within the module builder?

I have a custom module which we are importing, want to set multiple key identifiers for dedup when importing csv’s
Currently the dedup options are blank, I read somewhere I can update these in the custom folder but this would be wiped out when I redepoy the module

Cheers
DT