Does the garage have a window that you could enter through, possibly even if you have to break it out?
Depending on how tight the door is to the jamb and how tightly the tracks hold the door you may be able to remove the stop moulding or weatherstrip from the jamb, maybe even pry off the jamb board and gain enough room to find the latches and trip them. Sometimes older doors get so loose in the track that you can pull the door very hard from side to side while lifting and get the latches to release. You may even be able to remove some siding and or sheeting and go in through the wall. On an old wood panel door you might even be able to cut part of one of the panels out and repair or replace the panel after you gain access.
It all depends on how the garage was constructed and what kind of shape it is in. The fact is you are probably going to have to do some kind of damage to get in. The key is to find a way in, doing the least amount of damage you can or by damaging something that already needs to be repaired or replaced.
Depending on how tight the door is to the jamb and how tightly the tracks hold the door you may be able to remove the stop moulding or weatherstrip from the jamb, maybe even pry off the jamb board and gain enough room to find the latches and trip them. Sometimes older doors get so loose in the track that you can pull the door very hard from side to side while lifting and get the latches to release. You may even be able to remove some siding and or sheeting and go in through the wall. On an old wood panel door you might even be able to cut part of one of the panels out and repair or replace the panel after you gain access.
It all depends on how the garage was constructed and what kind of shape it is in. The fact is you are probably going to have to do some kind of damage to get in. The key is to find a way in, doing the least amount of damage you can or by damaging something that already needs to be repaired or replaced.
