We have a heavy wooden door leading to our garage which swings on self-adjusting hinges. It closed too fast and too hard so here is how I adjusted it.
First, use something strong and small enough like an allen wrench to slide into an open hole.
Next, pull back releasing the tension on the cylinder.
Use a pair of needle nose pliers to remove the metal stud which holds the cylinder in place.
Now place the metal stud into a new hole and release the cylinder gently. If your grip slips, the allen wrench can snap onto your fingers like a mouse trap, so be careful and use those pliers.
Make sure to adjust both hinges to equal tensions and you’re done.