set-window-start

set-window-start is a built-in function in `C source code'.

(set-window-start WINDOW POS &optional NOFORCE)

Make display in WINDOW start at position POS in WINDOW's buffer.
WINDOW must be a live window and defaults to the selected one. Return
POS. Optional third arg NOFORCE non-nil inhibits next redisplay from
overriding motion of point in order to display at this exact start.