To get to the Photos Repair Library tool on your Mac, follow these steps:
- If Photos is open, close the app. Then, while you click to open Photos, hold down the Command and Option keys at the same time.
- In the window that opens, click Repair to start the repair process. You might be asked to enter your user account password.
The Repair Library tool analyzes the library's database and repairs any inconsistencies it detects. Depending on the size of your library, the repairs might take some time. When the process is done, Photos opens the library.
If you repair a library that's used with iCloud Photos, iCloud checks the library after the repair process completes to ensure everything is synced correctly.
If these steps still don't work, or you can't open the repair tool, contact Apple Support.