Home the z axis of your 3d printer.
3d printer bed level gauge.
Sample of tool usage is in last part of video.
Now level the print bed the same way you do with paper.
A piece of ordinary office paper cut down to about 100 mm x 40 mm should work.
Here is a good starting set of tools needed to maintain your bed level and nozzle gap.
Repeatable method of leveling a three dimensional printer bed by placing a feeler gauge thickness gauge blade between the extruder and the bed.
If it homes to z max then send it to z 0 manually.
For 3d printer bed leveling and nozzle gap adjustment you ll need a card of a size you can comfortably hold and slide between the nozzle tip and the build plate.
This is all in one video of published bed leveling tool that i posted on thingiverese.
Start by tightening down all the screws so you have more room to work with.