Perform updates of Mainsail, Klipper, Moonraker and your system from within Mainsail.
Add the following section to your printers moonraker.conf:
[update_manager] [update_manager client mainsail] type: web repo: meteyou/mainsail path: ~/mainsail
Once you have restarted the moonraker service, the Update Manager will appear in Mainsails machine settings.
You can find further information on this topic by checking out the Moonraker documentation.