Welcome to the Bunnings Workshop community @152046. It's great to have you join us and many thanks for your question about repairing vertical blinds.
When you mention the bottom of the blinds has come undone, are you meaning the hemmed section that holds the bottom weight? If so, you could potentially use Moroday 24mm x 50m Clear Double Sided Hi Tack Polyester Tape. However, I believe it would work best if you got a needle and thread and placed at least a couple of tack stitches on either side of the hemmed section to hold the bottom weight in position.
If it's another part that is broken, perhaps post an image so our members have a better idea of what solutions they could offer.