Tie the leather like a knot
Where the leather goes through the stirrup to attach, wrap the leather around like a not and that usually makes it a lot shorter!
^^^^^yes i agree best was as you can change the length whenever you like. The part where you adjust your stirrup undo the buckle and then the leather that's already been put in the stirrup, wrap it round again. And then just adjust your stirrup as normal. Might sound confusing but theres probably videos on YouTube if you search putting a loop in stirrup x
We just roll them around where the stirrup leather is already going through the stirrup iron at the top of the iron to make it shorter.