how do you level a turntable?

If you can remove the TT feet, you can replace them with adjustable ones. If you can't remove them, maybe you can use some other form of adjustable isolation. There's also TT wall shelves.

You need a bubble level and some shims to insert under your TT feet. I've used layers of electrical tape with good results, but anything will work. It just needs to be thin so you can gradually increase the height.

I used 'Post It Notes'
Just take a pad of Post It Notes and start peeling off layers... place a few here or there under some feet and after a little fiddling you too can have a level turntable.