what kind of treadmill is it name brand and model not enough info to help. Sounds like you need to adjust the MAX VR speed but without the type of treadmill don't know where it is located on your machine. Try going online to the manufacture and get the FAQ for this they will give you step by step instructions
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix gym/fitness equipment.