nothing if you are not too worried - there is no reason why your t shouldn't be able to get out on its own, or is there?
if you are really worried, you can go ahead and dig it out carefully - you can use a small plastic spoon. and when you found your t, you can take the chance to change the substrate to something more stable. a mixture of potting soil and a little bit of sand (no more than 20%) works very well for burrowing species.
What kind of substrate is it and how deep is it? If it isn't too deep, or the T was near the top of the burrow when it caved in the T can probably dig it's way out. Even with that in mind, as has already been said, since it's already destroyed, I wouldn't worry about digging it up (unless it was an OBT or something that could really surprise you that is!). Be careful while digging though. It only takes one wrong move to injure the T or for it to suddenly come flying out of the substrate with your finger in it's jaws. I would recommend taking it VERRRRY SLOW and look for any movement after each spoon of substrate you move. Good luck with it and keep us posted.