You can update your email address in your app.
Go to More > Settings > Profile > Email > Click on "Update"
Once you do, you'll be getting a message to your new email address. Once you click the link to confirm, your email address will be updated on file.
You will need to enter your password and your Passcode in order to update your email address.
Your Passcode is the 4 digit number you need to get into the KOHO app (if you don't have touch ID or face ID). Learn more about how to reset your Passcode.