Don’t worry about technique, or gaining strength for your left arm, but get a punching bag or a soft object that can take damage, and hang it within your hands level. Use only your left hand to punch the bag, and punch softly, so you don’t damage your hand. We are only using your bare hands. Keep doing this until you feel any tiredness in your left arm. The goal is to gain coordination with your left arm.
You can follow these technique if you’re not sure how to punch
If you don’t have a punching bag, then you can use what’s most common, like a backpack.
You can probably get a string on the bag, and hang it on some sort of hook.
Or you can hang it on some sort of object like a tree branch.
