IBM Selectric Operating Instructions Manual page 34

Replace the Platen:
To
the platen the ratchet end
Hold with
-
right. This the end
is with the Page-End
Indicator.
Be sure that the shiny chrome face
-
the Finder
Line is
facing you.
Place the groove the platen
of
-
Platen Latch.
29
Press down
-
the
to will into
snap
of
the right
in
both Platen Knobs. The platen
on
place.