You can fix it by applying a screen patch, but I’m not crazy about how that looks. I’d rather replace the screen, it’ll take a morning or less if you buy supplies beforehand.
Measure the screen size and hit the local hardware store, where they’ll cut you a replacement screen while you shop for a small roll of vinyl screen spline and a spline roller altogether, these purchases should cost you less then $30. At home, remove the spline from the damaged screen. you’ll probably need a screwdriver or pliers to get it started, then you can remove it by hand. Remove the old screen and put the new one in place, it should overlap the screen frame. Use the round end of the spline roller to press the new screen into the frame grooves. Then use the grooved end to press the spline in place, beginning at a corner and keeping the screen tight as you advance. Cut off the excess screen a spline with a utility knife, and you’re good as new.