It is a really easy fix for a DIYer familiar with drywall and taping:

• Cut out out the damaged area in a rectangle (be careful of electrical wires that my be behind the drywall)
• Cut a piece of 1/2" drywall to the length and width of the cut out piece (snug fit)
• Apply drywall compound on both sides of all the joints
• Embed drywall tape over all the joints using a drywall knife (remove any excess compound as that will reduce sanding and dust later)
• Sand smooth and add more coats to achieve a wider smooth joint all around
• Apply primer the over the repair area
• Apply finish color paint