Take your bird to the kitchen sink. Take everything away that will be contaminated by the bird.
Run WARM water and put your birds butt in the stream. Leave it there until everything is washed away. Take a really good look at the opening (there is only one). Gently, gently squeeze around this area. Take note at how the bird reacts.
Look for prolapse, any blockage and presence of worms or insects.
This is going to be a commitment for you. You may have to clean the birds butt several times a day.
Guinea fowl are usually VERY hardy birds, even the babies.
Make absolute sure that you have not torn the skin. If you have then you will need to treat this.
Please let us know what you find.
You have done the correct thing, repeat, repeat, repeat.