Fix your wall mounted twin gauged mixed gas regulator to the wall near to your barrel(s).
Connect the lead to the bottle and gas line from the regulator to your keg coupler using the Gas Inlet Valve.
Set the gas pressure by turning the screw on the regulator clockwise.. About 30 psi should be enough..
There's no set rule for pressure because of the variables such as ambient temperature and dispense levels..
The main thing is to make sure there's no air in the beer line from the barrel to the cooler.
To check bend the beer line and if you can see bubbles in the line add a bit more gas.
Its the release of the bubbles in the line that causes your beer to FOB.
Lots of people make the mistake if turning the gas down when the beers fobbing.. This just makes it worse.
If your using 2 products you can use an (in line 1-2 line splitter). Or to feed 2 or more barrels its better to use a (wall mounted T switch ) for each barrel..
These will let you switch off the gas to any barrels not in use.