adding, removing, managing instances

Excellent app, and possibly the most stable on a slightly outdated tablet.

I would like to know how to add or erase instances listed, or are users limited to the three you offer (lemme.ee, lemmy.world, and lemmy.ca)

I have a custom/private instance I use the web interface with for a small group of developers, and cannot for the life of me figure out how to add it to connects list. Plus, I don't use lemm.ee or lemmy.ca, so I would like to remove them.

Could someone point me in the right direction?

Thank you!