To change the approver for a Challenge, you will go to Manage Awards > Challenges > Manage Challenges.
Then find the Challenge you are wanting to edit and click to edit.
If you are wanting to do multiple challenges at a time, you can use Bulk Actions.
Scroll down to the Claim Approvals section.
You can remove the existing approver(s) by clicking the trash icon next to their name.
In the search bar, you can search for the individual(s) you are wanting to add to the approver list.
Click on their name and then they will be added.
Then click the Save Challenge button to apply your changes.