Pump for 10 minutes rest for 10 minutes and repeat for an hour and that should help increase the supply in the one that’s lagging for lack of a better term also heat helps and apparently even just thinking of your baby, hearing your baby or any baby cry, and even smelling your baby can help trigger the let down of the milk
Also try to alternate positions as well as sides to help ease the strain on your nipples. Massaging them during the feed helps increase production as well. I have used the haaka and was none too impressed tbh if you have health insurance go to Aeroflow.com and order an actual pump for free 🆓
Yeah they tend to prefer one side over the other but just try to rotate as much as you can id recommend