Is that a flap of skin underneath the wound?
Was this caused by a roosters spur?
You need at minimum some Chlorhexadine spray or liquid, some lint free medical swabs and if you can get some, some triple antibiotic ointment.
Spray the wound with the Chlorhexedine and leave for 20 minutes.
If you have some vaseline, or medical petroleum, coat the feathers around the wound and lay them down away from the wound so the don't get in the way.
Soak a medical swab with Chlorhexedine and gently scrub the wound making sure you remove and debris and necrotic tissue. You can expect it to bleed a little.
Spray again with Chlorhexedine and let the liquid dry out. Once dry, apply the triple antibiotic cream making cover to the wounds edges. Just having a cream covering the wound will help keep infection out.
If the is a flap of skin unless you can stitch it may be best just to leave it hanging. The wound will fill in and make it's own skin eventually.
If you have a rooster then you will need to keep her isolated for at least a week, or isolate the rooster until the hen has recovered.
Again, if it is a wound from a roosters spur then you need to file the points of his spurs. You just need to make the ends round, nothing more.