If you already have an Ethereum wallet, then you can easily import it into Rainbow!
One of the big differences between Web3 and the traditional internet is that you actually own and control your own stuff. Your wallet is your "account" and you can instantly move it someplace else using its secret phrase (or private key).
Step 1: On the first page you see after downloading Rainbow, press the “I already have one” button
Step 2: Press the button labeled “Restore with a recovery phrase or private key”
Step 3: Enter the secret phrase (or private key) of your existing Ethereum wallet
Step 4: Tap the “Import” button