Don’t force them while on the car, you could break them AND damage the bodywork
unclip the plastic cover at the base whch reveales the screws securing the mirror to the door.
Remove mirror and take to workbench.
CAREFULLY remove glass by unclipping the black plastic surround.
This will reveal the ball and socket. Apply penetrating oil & then adjust, using PROPER sockets DO NOT BODGE WITH OPEN ENDED SPANNERS.
I adjusted the mirrors so that they move easily enough to be able to fold them as they are very vulnerable in car parks and when venturing down narrow lanes, yet firm enough so they don’t move at high speed.