How to make different piano hands different volumes?

I'm working on a song I found that has no piano covers and at the start, you can hear the left hand and the right hand fades in until it is louder than the left hand. But when I try to put it in and play it, both hands sound the same volume and both get louder. I wanted the right hand ppp and crescendo to f while the left hand stays mp, to be more specific. I tried to make the dynamic range to stave but it still didn't work. I've looked on other posts related to this topic but I have found none that solve my problem. Does anyone have a way to fix this?