Use a tire pressure gauge on the air bag fill valve.
__________________ 2000 Winnebago Ultimate Freedom USQ40JD, ISC 8.3 Cummins 350, Spartan MM Chassis. USA 1SG, retired;PPA,Good Sam Life member,FMCA. "We the people are the rightful masters of both the Congress and the Courts - not to overthrow the Constitution but to overthrow men who pervert the Constitution." Abraham Lincoln
Greetings Robin,
I see you have a 2021 Minnie Winnie 26T. Yes, as Ray has stated, you use a tire pressure gauge, but the 26T did not have a factory option for lifting bags. I suspect you might have two fill points; one for each side, but you may need to trace the air lines from the bags to the fill point(s). Whoever installed your lifting bags wanted the fill valve(s) to be easily accessible, so it (they) must be there somewhere.
Welcome to the forum.
Eagle5
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2019 Minnie Winnie 22M on an E-450 frame