dkonlineuse

Your photo has some severe scratching, so I'm not sure this will work for all of the marks, but it does well for dust and particles:
 
Create a duplicate of the layer that contains the photo, and put it above the original
Apply a Gaussian blur to the top layer
Apply a Layer Mask to the top layer, and fill with black
Using the brush with white on the mask (not on the blurred photo), paint the individual blemishes
 
This is a non destructive method that requires some trial and error to determine the best type and amount of blurring, brush size, etc.

Hi dkonlineuse

Welcome to the forums! :)

I would suggest resetting the app - just hold down the CTRL key when opening the app then click 'Select All' and "Clear" 

This should do the trick!

J