I know some swear by steamers and blow dryers, but I wouldn’t go that route as the heat is difficult to control and you could possibly damage the leather if too much heat concentrated in one spot.
I completely reversed the chains dents on my friend’s boy bag with some leather conditioner, felt, a heating pad, and time. Her boy has a solid lambskin back, no quilting or other stitching, so the thick heavy boy chain left some very large, deep indents on the bag. I looked at it and cringed thinking there would always be some damage.
I applied leather conditioner to the damage, wrapped the area in felt, set the heating pad on low and placed it over the damaged felt-covered area. Every 30 mins or so, I removed the heating pad, massaged the warm leather with my fingers, applied more conditioner if needed, and put the heating pad back on. I let the bag rest after a couple hours. I did this for a few days and if you saw the bag in person, you couldn’t tell where the chain dented the bag. I am usually skeptical of fixes and not always happy with the result as I have perfectionist tendencies, but I was shocked at how well this worked and how the end result was so flawless. You bag doesn’t look nearly as bad, so I think it would work for you very well in a shorter period of time.