I can’t speak from experience on the care of the break, I’ll leave that to those who have successfully healed them.
What I can offer is that you do need to correct your lighting, and supplementation, ASAP. That is a large part of why you have the issue you do. Coil bulbs and time by a window are insufficient for a cham....windowsblock uvb rays, that’s how we do not get burned through them. You need linear lighting and calcium without d3; d3 is fat soluble and they can OD on it. If you opt for t8 lighting instead of t5ho you will need the calcium with d3 every other week only. Too much will be counter productive. You’ll also want a multivitamin every other week.
The white from the nose is excess salts, it is not related to lighting. The correct lighting and supplements will treat the underlying MBD, which is what lead to the fall and fracture.
Pet stores often give bad advice, please know people here only want to help you and your cham. Many of us get bad info at first, you are not alone! Please fill out the help form posted so you can get the best help possible. Details are important with these little guys.