The quality of the level doesn’t matter: almost every level has some error. I used to install medical research centrifuges that spin at 80,000 rpm*, and at those speeds, perfectly level is critical.
Step 1. Place the level about halfway in on the platter. Note the error. Now, don’t touch the level but rotate the platter 180 degrees. Note the error. Now you can adjust the table’s feet to get the table level by making the error the same but opposite at both points. Rotate the platter 90 degrees and repeat.
Step 2. Move the level 90 degrees around the platter. Repeat the above. Ideally, even if the level is off by half a bubble, you can have that same half a bubble error on the OTHER side of the level when you rotate the platter. If the bubble is just outside the center circle on the left side, then it should be just outside the center circle on the right side after your rotate the platter 180 degrees. Keep adjusting the feet until the bubble is off-center by the same amount in the opposite direction when you rotate the platter 180 degrees. Repeat 1 and 2 until any remaining errors are equal but opposite.
This takes a bit of time, but the results are independent of any error in the level, minor inconsistencies in the platter, any issues with the spindle or bearings not being perfectly aligned, or how level your floor or turntable support is.
* To reach those speeds, the chamber was in a 3-5 micron vacuum, refrigerated, and the “motor” was a small oil turbine driven by 300 psi of pressure with special non-flammable hydraulic fluid.