I recently purchased a 3 function remote #139.53778. I have two Craftsman garage door openers a model139.53615SR and a model 139.53500. I was able to easily sync the opener to the 139.53615SR by using the smart button or learn button on the opener, however the model 139.53500 does not appear to have a learn button and I cannot figure out how to sync my new remote to that opener. I have not been able to locate a manual on-line. Do you have any advice to offer?