how to add existing named people in photos back into people library

Hey Sc00tr,

You can find the steps to add names to photos for people in your Photos Library here: Find and identify photos of people in Photos on Mac - Apple Support

"Manually identify and name people in a photo

Some photos may contain people who are not automatically named. You can name them manually.

1. In the Photos app  on your Mac, double-click a photo to open it.
2. Do one of the following:

• Choose View > Show Face Names. Click the name (or click “unnamed”) under a face, type a name, then press Return (or choose a name that appears as you type).
• Click the Info button  in the toolbar. Click the Add button , drag the circle to position it over the face if necessary, click the Name field, type a name, then press Return.
  • You can click the Add button  multiple times to identify multiple faces in a photo. To remove a name that you added to a face, click the Remove button  on the person.

To stop showing face names in photos, choose View > Hide Face Names."

Thanks!