The 13953879 number is for a remote, which I am assuming is the part of the opener that was misplaced. You can order the remote direct through the Sears Parts site using the model number of your opener itself, which will be the "139" model number listed on the overhead unit, and the instructions in the link below. Or, you can take the 13953879 remote number to your Sears Store to get a replacement there.
Once you have the new remote follow the instructions on the overhead opener, or in your manual, or in the other links below to program it in. If you have problems getting the remote programmed, be sure you have the correct remote for your opener and all the remotes and the keyless entry have good batteries in them. If so and the remote still will not program then the memory on the opener might need to be reset. Again, the procedure is in the manual and the links below.