At the rear end of the torsion bar there is an adjuster cam and an adjuster bolt that positions it. That will give you some adjustment. Just be careful with those bars ... there is a lot of force there.
Before you adjust the bar, make sure there isn't another problem. You shouldn't have to adjust the bar tension unless the adjuster was moved -- and that shouldn't happen on its own. Maybe something with the adjuster (or even the bar itself) broke on that side. Compare to the other side if you need a reference.