Caveat: I've never done this myself.
My instructions (maybe the same that you have), however, say that all the adjustments are to be done from the front, left-hand side of the enlarger. They also say there will be "considerable counterclockwise spring force on the tube," which would indicate that if you want to tighten the tension, you would turn the tube in the opposite, i.e., clockwise direction. I understand that as meaning rotating a point on the tube from the top, down around the front and then up the back of the enlarger to the starting point to make one clockwise revolution. Beseler says to start with two turns if you need to tighten the tension.
I'd be real careful I didn't lose my grip on the tube and have the whole thing unwind to zero tension... zzzip... before I could get a hold on it. Maybe you can rig up some kind of stop with a long clamp that would jam against something and prevent the tube from rotating (with some appropriate padding so as to not damage the tube, of course).
Beseler also says to never loosen the screw on the tube itself; you likely know this already, but I thought I'd add it just in case.
Best,
Doremus