my four wheel drive is struck in low how do i get it back to two wheel drive

The encoder motor has to shift the transfer case. You can try having the truck stopped in park with the brakes applied. If that doesn't work, reverse a couple feet and then put the transmission in neutral and again with the brakes holding the truck attempt another shift out of 4WD low. If that doesn't work then you are going to need a scan tool for diagnostics, it's likely that either the 4WD module is detecting a fault and shutting the encoder motor down, the encoder motor and its feedback system has failed, or it could be a problem inside the transfer case.