I nicked my strop pretty deeply today, again! I should have taken a before/after shot, I will next time.

My steps to fix:

Pull the cut flap back (about 1/4" wide cut) and put contact cement on both sides (the flap and the base leather). Let the contact cement dry BEFORE you put the flap back down (about 15 minutes). Put the flap back down and go over it a few times with a wine bottle to smooth it out. Still a lump?! Sand the spot with 320 grit till you don't feel the lump and finish with 600 grit till absolutely smooth. You can sand quite aggressively and not harm the strop. I then rub the leather with my hand using only the oils from my hand till it is the same color as the rest of the strop. End result, you can't even tell it was nicked and it is as smooth as ever.

I also used 600 grit to sand away any small little nicks along the edge. A few strokes and they are gone.

Don't get stressed out when you nick your strop, it's easy to fix!