Repair L-shaped notch in drywall
Hopefully there was a notch drilled in the plate, so that when a wire staple is set it will pull the wire in behind the face of the drywall. It should have been cut out large enough to allow a metal plate to cover the wire to protect it, although it is unlikely there will be any nails or screws going into the corner right there, but you never know....

Anyway, after the wire is held in place with a staple, pack the slot with drywall mud if you prefer, but it will take a long time to dry, unless you use a fast setting type and scrape that flush with the wall, do not allow that to build up or sag. Add another layer of mud for a setting bed for the tape, whether it be paper or mesh. Set the tape over the whole slot, running it into the corner and out onto the wall and ceiling. It may be a little tricky, but you can do it. After that has set add you finish coats, let dry and sand smooth.