If you can get the serial number and model number from your garage door opener, via ladder or binoculars or whatever it takes, you should be able to download a user's manual from the internet. Just google it. I have done it with many different tools my husband has picked up at auction and most sights are free. It is helpful to print it off and stick it in a file for further reference.

The most I have paid for even a rebuild manual was $5.99.

Here is a link that might be useful: A link to get you started