Find "x", count up and store # of rows

[ker9]

How would I write something that would

Do Loop

start at bottom (xlend) and work up

Find "GroupChange" in column N (0,14)

Count rows UP to next "GroupChange and store number
(can store it in column O on same line as found GroupChange)

Maybe insert a blank row after GroupChange to insert formula that uses that number of rows (sum up x rows)

until it can't find it

Thanks!