Leave a shared reminder list on iCloud.com
To stop participating in a shared reminder list, you can leave the list.
Note: If you’re using upgraded reminders, you might not see all of your shared lists on iCloud.com. You also can’t manage sharing on the web. Use the Reminders app on a device with iOS 13, iPadOS, or macOS Catalina 10.15 to see and manage all your shared lists.
In Reminders on iCloud.com, tap the broadcast icon next to the shared reminder list you want to leave.
Tap Leave List, then tap Leave List again.
To join the shared list again, ask the owner to reinvite you.