Thanks for pics.
Please pick one remote that works with your current opener which you're willing to use for interfacing.
It will have to be opened to expose the PCB inside. If there are no screws accessible through the battery compartment, typically there's widening in the seam that can be used to prop the case open.
Please post the pictures of both sides of the PCB and I'll point out the connection points for the Garadget's control wire.