Sygic volume too loud

[keith89]

I'm trying to figure out how to adjust the volume for Sygic Nav. There is no volume function in the app. Sygic is my default GPS app so i went to the joying factory settings(3368) and adjusted the volume mixer. I turned the gps volume down to 1 or even 0 and it did not make a difference. Any suggestions?
My unit is: JY-UO135N4GS
Purchased mid August. I have not done any firmware updates etc.