What kind of platen press is it? Is it a tabletop press or an 8x12? If so, I highly recommend John Folstrom's platen leveling tool:
We just used that to level the platens on our two old rustbucket rescue C&P Pilots and it worked great. Very little physical instruction needed; it's pretty self explanatory (my additional note not included on the instructions: take the chase out while you're there removing the packing from the other side). The site says the tool will work on a press up to a C&P 8x12. Worth every penny and it was practically next-day shipping.
If your press is larger, I'm not sure how else to help! Sorry!