Pivot Arm detached from bottom of Hehr window - help

We have Hehr frameless windows that have a control knob that connects to two pivot arms to open and close window. Pivot arms have a white disc that fits into the bottom frame of the window. When closing our window both discs jumped out of the track. Anyone know a trick to get them into the track without pushing out the rivets and then reinserting them and somehow re-riveting the control arms back on. Note: discs would fit into the end of frame channel; however, they will not reach that far. Any way to lube them and somehow force them back into place?