Invisalign Express for One Crooked Tooth?

Yes, Invisalign should work to move one tooth provided there is a reasonable amount of space to move it in to. It is also possible that a flexible, adjustable retainer could accomplish the correction. Your orthodontist will be able to answer this question at an initial consultation.

It is possible to correct one crooked tooth
with Invisalign Express. However, it is important to note that other issues
such as the bite would not be corrected in this process.

 I  would start with the cheapest and simplest way first.  You wore braces and had great results. Then you stopped wearing your retainers since the first year of college. Not a good choice...but it happens to many. I would first try a retainer that is adjustable and flexible to  move that tooth back into the position it was after you had your treatment with braces. If this does not work, then go to inivsalign express. Remember, what ever procedure you choose, me mindful  if you want to keep your teeth straight and not move, you must wear your retainers for the rest of your life or they will eventually migrate back to where they came from! This goes for invisalign and vivera retainers as well as regular retainers that you stopped using after successful movement with braces.  Good luck on that one tooth!