How do I increase drying up milk supply?

I've been trying for the longest but I'm not with my baby all the time and have never been that adequate at feeding him fully with out needing to supplement the rest. So when I'm away SO formula feeds. My baby is 4 weeks old and im only able to feed him fully once a day I also take lactation tea chews before I breast feed to help. Also doing my best with a hand pump sometime it doesn't feel like any help any advice? I'm worried my chews aren't helping anymore like they used to aswell.