Standard size outer mirror

Put the mirror side down.
Insert a thin screw driver, push the clip part of scalp cap, and then remove the scalp cap.

Fig 1: Pushing Clip Part Of Scalp Cap
Courtesy of SUBARU OF AMERICA, INC.
Insert the claw at the lower side of scalp cap to the door mirror.

Fig 2: Identifying Claw At Lower Side Of Scalp Cap
Courtesy of SUBARU OF AMERICA, INC.
Install the scalp cap securely.