To clean your leather sling bag while making sure that you do not mistakenly damage its overall finish, you should use these cleaning steps:
Before you start cleaning, carefully check the instructions mentioned on the care label so that you can choose the cleaner or conditioner according to the instructions.
Instead of applying the cleaner to the entire sling bag, you should try it on a small spot to check whether it causes cracks or damage.
You should avoid regular household detergents and use mild cleaners and conditioners that do not cause any damage to your bag.