There will be a visible triangular shaped plastic molding in fron of the mirror, pop that off, there will be screws or bolts to remove the mirror. Didn't the replacement mirror show diagram, or did you buy a used one from a bone yard? I hope this works for you.
Begin by removing the inside passenger door panel. Remove the wiring harness from your passenger side electric mirror. Remove the mirror retaining bolts. Reverse the process to install your new electric passenger side mirror.