You'll start with clicking the 3 dots in the upper right-hand corner and tapping Settings.
Then, you'll click on Privacy & Security.
From there, you'll then tap on Wallets & Keys towards the bottom.
Next, you'll select/click on the wallet you're looking to remove.
Then, you'll click on the 3 dots next to the wallet name and select the "Delete Wallet" option.
A prompt will appear that has you double-confirming the removal of that specific address. Once confirmed, you can click Remove and the wallet will be deleted from Rainbow.