Here is a download of the Yamaha Mio 125 Parts Manual from Yamaha. I had a helluva time finding it, so you shouldn’t have to go through the same.
If you want to know how to adjust the idle on your Mio 125 – just lift up the seat. Remove the rubber seal on the hump there. Use a long screw driver and turn the screw clockwise to cut the engine rpms a bit. Turn counter-clockwise to let the engine rev a little higher at idle.
DOWNLOAD Yamaha MIO 125 Parts Catalog below: