WARNING: read the instructions carefully, you have to assemble bearings in the correct order, otherwise you will encounter problems later!
⬢Take the first bearing and place it in the middle of the idler. Insert the shaft as in the picture, make sure you are using the opening on the top.
⬢Slide the shaft in using 2.5 mm Allen key. Make sure the shaft is all the way in and not blocking other slots for bearings.
⬢Take the second bearing with the shaft and assemble it in the same way as the previous one.
⬢Take the third bearing with the shaft and place it in the idler.
⬢Make final a check, ensure all three bearings can rotate freely.
⬢There are small openings on both sides of the idler, which can be used to push the shaft back.