Calibrating a resin printer
First of all a caveat:
Leveling an FDM printer
...is done differently than an SLA/DLP printer
When calibrating an FDM printer, you align the bed with the X and Y axis, using a paper, metal shim or another tool (such as a feeler gauge) to make sure the plane that the nozzle moves in is parallel to the bed as much as possible. The paper, shim and gauge all serve in making sure that the nozzle does not push into the bed on the move and to be an easily measurable system. You need to do several measurements and repeat the process till the bed is level. This can take quite some time with paper or shims, which is why I use a feeler gauge in the micrometer area.
Leveling an SLA/DLP printer
when leveling an SLA/DLP (aka Resin) printer, you also want to align the bed, but you want to align it parallel to the screen. The process is rather simple: mount the bed and loosen the retention mechanism, have the printer move down and press the bed against the screen surface. Some printers need to have the (preferably empty and clean) vat installed, others need you to remove it. Tighten the retention mechanism. Move the bed up, you are leveled. Only now comes the resin (and vat!) back. Some printers have their leveling mechanism separated from the mounting screw - that allows removing the bed for taking off the part and keep the leveling intact.
In the case of the Creality ld-002r there's a video Tutorial, the alignment screws are on the side of the carriage. Remove your resin vat before leveling. Loosen only those side screw, keep the top one fast!
The reason why I suggest to level against an empty vat is to make sure that on the one hand the resin doesn't go bad (it should be exposed to as little light as possible), you are exposed to the least resin fumes as possible and to make sure that no pieces are inside the vat when your printer firmly presses the bed against the screen - it could damage the screen or surface would there be chunks of former prints left in the vat! Also, you don't want to contaminate your tools with resin, which means you want to work on the fasteners with no resin in the vat.