how to put mirror head on mirror base

if htis is the mirror inside the car, the metal piece is held on by a screw and then needs to be taken off, clean glue off normally with a knife/sharp object. and then you can buy the glue anywhere they sell autoparts. it's a little tiny tube. follow instrucktions on glue box. if it's an outside mirror glass shops normally charge around $20 and do it on the spot.