To unapprove or unaward an advancement in Scoutbook Plus. First you need to Unapprove it, then approve it again.
Click on the Scout’s name in the Advancements > To Purchase section in Scoutbook Plus
Click on the > icon next to the advancement’s name

Check the box next to the scout name and in the grey bar look for Unapprove Item. Click on that and it will un-approve the selected item.
You can also un-approve rank, awards and merit badges at the scout profile page by selecting the item. One in the rank, award or merit badge you would remove the date by hovering over the calendar icon and selecting the X and uncheck the approval check and click save

Confirm you wish to unapprove the advancement.
Then use the regular process to approve / mark awarded it again.