Add Assignee option is not allowing updating or deleting assignees

We have configured approval on addition of Pending Worker where the line manager of requester is going to approve the transaction. When the line manager receives the approval notification, they can see an action named "Add Assignee". When they click on it, they only see the option of adding assignees. The edit and delete icons are greyed out. We thought that it might be role issue and hence we assigned all super user roles to this line manager to check if Edit and Delete are enabled. But even after doing all that, this user is not able to click on