1) Open up the picture you want to use, to go with last chapters theme I went with Archie (Kj Apa) from Riverdale.

2) Use the burn tool. I set mine to zero hardness, exposure 30, and for the range you can use either shadows or midtones.

3) To get the best effect it's easier to zoom into the picture and start creating the bruise. You can go over the area as many times as you want until you get the desired look. Be careful because you don't want it to look unrealistic, keep in mind of shadows. Look up real pictures of bruises as inspiration.

4) That's pretty much it. You can then add any adjustments to the photo I brightened the picture up and messed with curves.