There should be a notch along the bottom or side that will accept a small blade screwdriver. I'm assuming you're talking about clearance lights. If there is no notch, use a knife blade to work it loose. With the usual precautions using sharp things. Wait, tabs- you're talking about tail-lights right? The tabs will break if the plastic is several years old, from sun-rot. I would go ahead and pry the lens off with a screwdriver. On my old RV I used a long sheet metal screw to hold the lens on until I could buy a new one.
2000 Winnebago Ultimate Freedom USQ40JD
, ISC 8.3 Cummins 350, Spartan MM Chassis. USA 1SG, retired;PPA,Good Sam Life member."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 theConstitution. "Abraham Lincoln"