Trace with a piece of charcoal or soft pastel, over the lead lines of the panel that will be restored.
lay the tracing onto the work space and place grid paper over the tracing. The grid paper helps to true up the lines, make them straight and create the pattern that will be worked from.
Next, start pulling off the old lead, and clean up the piece of glass then lay in the respective place on the pattern.
Next update will show the glass cleaned and in place.