When you only have one account connected, Reply will not allow you to delete the previous setup to place a new one.
There is a workaround for that:
- Open the Email Accounts tab of the Settings page.
- Click the Add button (+) to connect a new email account.
- Make this new email account your Default account.
- Delete your actual email account.
- Go to your sequence -> settings and re-assign the email account for sending.