How To Install Interior Window Sill Trim. Fit the window sill. The seams are usually covered by caulk and painted to create a smooth look so you are breaking that line of caulk.
Repeat for the opposite jamb. Once you get a hole you can pull it out in bigger chunks. Determine your window sill horn.
Use the pry bar to carefully remove a section of the window trim and check the insulation inside.
Attach the stool with countersunk screws. Remove sealant and adhesive residues. Away from the jamb at both ends and along the base of the window casing. Twice a year or as needed clean the trim with soapy water and let it air dry.