You can edit holiday approver settings at any time. To do this, locate the employee whose holiday approvers you wish to amend on the main holidays tab in your company settings and then click on the green edit button that will appear to the right when you hover your cursor over it. This will open up the same window used to set up the holiday approvers in the first place. Here, you can remove or add holiday approvers to that employee. 

If you would like to delete the holiday approver setting completely, simply hover your cursor over the employee whose holiday approvers you with to delete and click the refresh icon that appears next to the green edit button. This will prompt a new screen to appear. Click update to restore holiday approvers for the staff member to just their line managers and admin users.