The more often you pump the more you'll produce!
Pump as often as you can! You can try tea, I drank Mother's Milk when my supply would get low. Lactation cookies help too! Oatmeal helped a lot too, I would eat some every morning along with my tea. It will take some time and patience, but you can definitely get your supply back up if you stick with it
Just curious why you are pumping? Nothing will increase your supply more than your baby feeding directly from the breast.
Stay hydrated. That was always huge for me. Keep to a schedule and try to relax while pumping and think about what you are doing and why you are doing it. I found when I engaged my mind into pumping I would do better. People on this forum have talked bout fenugreek to help boost supply, or a mother's milk tea. Best of luck!