I only see the option to change active pet, but would like to assign battle pet to another. How do I do this?

If you're talking about the sidebar gadget I'm afraid you can't do that, the battle pet will always be your active

unfortuantely that's not really a thing. if you only want to battle with one pet, you can just keep them checked into the resort/inn and let the rest of your pets stay hungry so it'll be the only one listed as eligible for battle. you can also keep your battle pet at the top of your pet order so it shows up first on the training page.

I did mean for the sidebar, that's unfortunate I can't though. Thanks for your help c:

I'll do that, thanks for the advice!

Could also add it as a suggestion and maybe staff will create an option for it ^^

It's been suggested when the Item Box got revamped that we be able to designate eaterpets battlepets readerpets and playerpets for those dropdowns. While staff was supportive of the idea, nothing has come of it.