How to tell if address is base

New to Ethereum, using Rainbow with ETH that I got from BTC using a conversion app (changeNOW). I guess I didn't notice that this time I chose ETH (base), whatever that means.

How do I know if the address I want to send this to now to make a deposit on a site is on Base? If it's not will the ETH go away forever?

And then if so what's the easiest way to switch this from Base to regular ETH? I don't have and can't use Coinbase.