Verified answer

Most garage door openers can delete all connected remotes by pressing the "learn" button for about 6 seconds until the learn LED light goes out, releasing the button then a second time pressing the "learn" till the light goes out.

Some only require the 6 seconds once, but twice doesn't hurt.

On mine you simply press and hold the LEARN button on the opener for six seconds to lock out all existing remote codes by erasing them from the receiver's memory.

It can't be done even with access to the vehicle.

You actually program the garage door opener to recognize the FIXED code from the remote. The remote isn't programed to the opener.

you may be able to change the codes used by all remotes inside the opener. see owner's manual. you'll then have to change your remaining remote [or a new one] to match

Change the codes on the garage door opener.

Change the micro switch code in the garage door opener itself.