There are many professional tools that will make the corner look perfect, such as the [product|IF145-280-2|gTool iCorner] or the [product|IF145-352-2|PlierTek Corner repair] pliers. If you’re doing this repair as a one-off, then any type of small smooth pliers ([product|IF145-414|Like this one]) will help bend the corner into the correct shape.
You should be able to get a basic pliers set at any local hardware or craft store.