Don’t worry about technique, or gaining strength for your left hand, but get a pump container with a long pump, it can be a empty soap bottle, empty ketchup bottle, and even an empty hand sanitize bottle. Anything that has a pump attached to a bottle. Fill the bottle up with water, and pump out the bottle to an empty container or anywhere where it doesn’t leave a mess, with your left hand. The goal is to gain coordination with your left hand

Keep doing this, until you feel any tiredness with your left hand.

Pump the water like this.