Make sure you are on a flat and level surface

Check that the frame is not twisted by pressing downwards, on each corner in turn.

If the frame is flat and does not wobble, you can continue to the next step.

If the frame wobbles, place a 5-10mm thick object under the opposite corner as shown in the 2nd image.

The small green arrows show the wobbly diagonal. It might be the other diagonal for you, in this case, place the object in the bottom right corner.

Apply pressure on the wobbly corners on both sides at the same time. There is no need to apply strong pressure.

Now remove the thick object and check whether the frame is now flat on the table. If it is still wobbling, repeat these steps until it lies flat on the table.

If the frame is still wobbling, double check that your surface is flat. If necessary, loosen all of the angle corners and repeat the previous step (Step 21) and then the current one.