You can try heating their faulty parts (presumably legs) with either a candle flame (accurate and relatively safe) or near-boiling hot water (more dangerous and certainly messier) - or, ideally, a heat gun. Heat the spot very gradually and keep the source of heat (if you aren't using water) at a sufficient distance to the plastic lest it burn or swell. (This means 10-20cm above a candle flame, heating the part during the course of a minute or more, depending on its thickness.)
Try the part occasionally to see if it bends readily. Once it does, bend it to the desired shape, then submerge the figurine in cold water to set it in its new position. If you need to bend closely situated multiple parts, do them one at a time and cool the figurine in between, so that the part you heated first doesn't re-soften faster than the second part you want to heat. You can bend a part multiple times without damage if you are careful enough.
This is a simple, quick fix for any balance issues with plastic models, especially the ones made out of the slightly bendy plastic (such as Papo, Schleich, Bullyland etc. as opposed to the cellulose acetate-based Breyer-type hard plastic). Good luck!