Reset Users Unshare desicions

Hello community. Thank you in advance for your support.
Here is my scenario:

  • the admin created a group “Group_A” and a folder “Folder_A”
  • the admin shared “Folder_A” with “Group_A” with full permissions
  • the admin assigned several users to “Group_A”
    Now one of the users accidentally unshared “Folder_A”. So far I didn’t find a way to let this user have access to this folder again. Somehow the account remembers the users “action of Unshare”. Is there a way to reset this?
    Thank you and best regards.