EV Index drive is almost full

thanks for time and effort.

This morning the storage and task controller service stopped.  When I checked the server the EVIndex drive was low on disk space..77MB left of 2TB. I was able to free up another 300MB due to non index files there.

I was reading on the forums to see if I can add an additional drive for the EVIndex. I wasn't clear on how to do that?  Do I need the storage added and then go to Add to Index Server Group? or is that adding a server only?

apologize for all the questions. thanks for the time.