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What to do depends upon what opener you have. Or more strictly, on what type of 'receiver' - on one side of the opener - your opener has. Whether it is a modern one with a push-button on it, or an ancient one with a bank of little switches on it, dictates whether to push that button to configure the wireless link between opener and remote, or to configure switches to match a similar switch bank in your remote (which is getting obsolete as a way to configure remotes to openers, so it is not likely that your remote has a switch-bank, even before I look up the specifics about it.)
The button to configure remotes to the opener, on the receiver, is usually square (generally speaking) and often either yellow-colored, or red-colored. Please look for it, and let me know what you find. Thanks.
(As for the light on the door sensor or floor sensor... that may need realigning of the sensor, which if bumped into and bent, will be out of alignment.)