Look around for a dark gray knob about 2 inches in diameter. On tthe suppoert tube you will find what looks like a dark grey 1 inch knob. Get a pair of needle nosed pliers and a magnet ( your safety key) place the magnet on 1" knob and a bolt will pop out about 1/8" inch. Grab it with the pliers and pull it out as far as you can. Grab the end with your fingers and reposition the pliers as close to the 1" knob as you can. Holding the bolt with the pliers, scfrew the 2" knob onto the bolt as tightly as you can. in the future, pull, don't turn, the 2" knob to lower the running surface. You will have to hold the treadpart up while you do this to take the weight off the bolt so it is free to move without binding.
The manual is available in PDF form on this site but it does't descrbe the problem.