Start by cutting out the skin inside the servo locations.
Peel off the skin carefully. The cuts should be at least 3mm inside
the outline. More if your servo is smaller and you want to reduce the
size of the servo pocket.
Pick out the foam inside the servo pockets carefully, first with a
regular X-acto knife, then using a spade knife when near the top
skin.
Clean the foam out completely, carefully scraping it off the top skin
with the spade knife. You need as much depth for the servos as
possible. You should see the wire channels in the corners of the
pockets now.