Model Without Side Turn Signal Light

Remove the mirror. < Ref. to REPLACEMENT , Outer Mirror. >
Press-in the clips (A) from inside of door mirror.

Fig 1: Pressing Clips From Inside Of Door Mirror
Courtesy of SUBARU OF AMERICA, INC.
Pull the scalp cap foreward of door mirror, and then remove the scalp cap.
Mate the backside clip (A) of scalp cap with the clip hole of the outer mirror to install, and then push the scalp cap in.

Fig 2: Identifying Backside Clip
Courtesy of SUBARU OF AMERICA, INC.
Install the scalp cap securely.