how to recalibrate my new digital dr trust weght scale?

there are no adjustments and nothing in the manual about recalibrating and the scale gives wrong reading and not even consistent reading. this is a 'platinum rechargeable digital weight scale 501', serial number P1908002396. it was supposed to show the letter 'c' after stepping on it the first time, then zero but it never did any of that. from the beginning it has done nothing but keep going up and down mostly above my actual weight and when it stops it is in the 70's and i weigh under 60. when i first step on the scale i see zero's, and when i get off the scale it will not go all the way back down to zero, it stops somewhere at random like 5.00 or 13.90 and flashes a few times then sits there until it turns off automatically.