FIND AN ACUPUNCTURIST who will do moxibustion on you. Works the majority of the time (like over 80% of the time).
Webster Technique was already mentioned. Also very good. If you are at the chiropractor, or if you/they know a myofascial release specialist, myofascial work on your belly will release any fascia that may be holding the uterus in some funky position that is keeping baby from putting its head down (or in any other non-optimal position). Plus, if you go the western-medicine route of trying an external version, it will be easier for them because your fascia will be loose and baby will move easier. My chiropractor does myofascial release on my belly and it feels SO lovely.
Shine a flashlight against the bottom of your belly. Play music at the bottom of your belly. Have someone TALK at the bottom of your belly.
Do headstands in a pool (easiest if you have someone with you to hold your ankles), making sure that you are under water at least to your thighs. Hold them for as long as you can hold your breath.
You can make your own inversion table by propping a (strong) ironing board up on a couch. Again, helpful to have someone there to assist you with getting on and off of it and make sure you don't get dizzy.
You can also do inversions by getting on your hands and knees and then folding your arms underneath you and resting your head on your arms.
BEST OF LUCK, mama, and remember, a breech baby can still be born vaginally!!