If you need to remove RMail app from Gmail, please follow these steps:
1. Open Chrome.
2. At the top right corner, click on the 3 dots menu next to your profile icon.
3. Click on the More Tools option in the resulting drop down menu.
4. Click on the Extensions option from the resulting drop-down menu.
5. Locate the RMail app for Gmail extension panel and either disable the toggle button or remove the extension