PSI

This is no different than the tow rating of any TV...a specification/rating/etc
are just that for whatever it is written for

Molded on the tire info is for 'that' tire, period

Trailer manual is for that trailer and the OEM tires it is supposed to
come with. But the molded in tire info trumps the manual or anything
else....period

That molded in spec is for the max weight, which is also molded in
the same area of the tire sidewall

So unless you are running 'that' tire at molded maximum side wall spec
the best tire PSI is lower...meaning do NOT go over the sidewall
weight rating

What that lower PSI is what I think you are asking help in figuring
and that means you need to know the actual weight that tire is
carrying...meaning you need to go out and weigh your trailer...axle by axle