Very confused about the seatpost clamp
Turning the lever will not tighten or loosen the clamp.

The lever is a handle to allow you to twist what would normally be a nut by hand - instead of using a wrench.

Using the lever as a handle twist push down on the lever and move the "nut" counter clockwise until it comes off.

Put just a tiny dab of grease on the threads of the bolt and re-assemble.
The grease will make it easier to get the clamp tight enough to hold the seat post - and protect against rust.

While you are there it would be good to remove the seat post completely and put a little grease on the seat post in a super thin coat and then re-assemble. This will protect the seat post from rusting to the inside of the frame.

If you have no grease a little oil is second best.