Four wheel drive will not engage

i don't mean to sound stupid, but this is going to sound stupid.
drain oil from where? oil pan? transfer case? I am kind of confused on your suggestion.
Sorry

thanks for your help

drain some of the oil from the front axle at the fill plug!

in the somewhere in the middle of the front axle there is what looks like a plug with a square hole, this can be taken out with a 1/2 inch racket, once you get the plug out get a smple of the fluid, don't need to much, put it between your fingers and rub them together if it feel gritty or you see metal filings then it could be the pumpkin like merlin 2021 mentioned