Here are the instructions on tagging a missed photo.
1. Open the Waldo Photos app and select the photo. Once it brings up the full sized photo, tap the photo to reveal several icons.
2. At the top of the screen you will see a “tag” icon which you can tap on.
3. A white square will popup on the faces that can be tagged. Tap on the face you wish to tag and a list of your names will appear. Tap the name of the face you wish to match and click done in the upper right corner.