Accept a shared reminder list invitation on iCloud.com
If you receive an email invitation to share a reminder list, you must accept the invitation to access that list.
Note: If you are using upgraded reminders, you might not see all your shared lists on iCloud.com. You also cannot manage sharing on the web. Use the Reminders app on a device with iOS 13, iPadOS 13, macOS 10.15 or later to see and manage all your shared lists.
Do either of the following:
In the invitation email, tap Join [list name].
In Reminders on iCloud.com, select the shared reminder list on the left, then tap Join or Decline on the right.
After you have accepted an invitation, you can view and edit the shared list and all participants see the changes you make.
Note: Only the owner of a list can add or delete participants.