There are times where the tonearm lifter may drop too fast or not drop at all. Usually a simple adjustment is all that's needed.
If the tonearm lifter isn't dropping
You can free up the t-bar by loosening the flathead screw located on the top of the mechanism, and then moving the plastic part up and down a few times.
You then gently tighten the flathead screw to return the t-bar to its original position.
If this doesn't solve it, it's likely that the lever isn't catching correctly.
If the lever isn't catching correctly, the unit will require a physical repair.