Adjust volume

I have gone through the codes for my Hisense tv and have found the code and my slimline 2 remote will turn the tv off but I can’t get it to adjust the volume. If we watch streaming apps such as Netflix  using the Telus box we have to have the volume on max but if we watch using the apps through the Roku tv the volume is less than 20 so it’s the Telus box volume that needs to be adjusted but we can’t get that done