I would like to lower the volume of the channels on mixer. I can link all channels and lower the volume, however there is a lot of volume automation on different channels. Is there anyway to link and lower and make the automation be relative?
There’s a master fader for that purpose 
Or select all automation points (PLE) and use the info line.
I usually do in the pre section by subtracting desired amount on each channel through gain. If I example select gain click on type in -2db. you can send all to buss (inst buss) (vocal)etc and lower that way
+1.
Also: if you like to keep your master fader at 0dB, another way is to turn down the input gain at the top of the master output channel (I’m not sure if all Cubase versions have that).
Finally, and this one works for all Cubase versions that can create groups: You can create a group called “Final Volume Control” which is routed to the master output, and route all your tracks to that Group instead of the master output. Then you can change the fader on that group. This way also keeps the master fader at 0 dB.
For some reason I’ve wound up using the last method. Though I’ve just started something new, trying to make it redundant by paying close attention to gain staging of each track. Not sure it’s necessary in the digital environment, but if nothing else it keeps me focused on levels.