Hi,
@MissDawn - do you mean that the nib is falling out of the flange? or that the flange is falling out of the holder?
If the flange is too loose for the nib, you can tighten it by bending or pinching it a bit with some needle-nose pliers.
If the flange is coming loose from the holder/grip, fixing it will depend on how it's held together:
Sometimes there's a little bolt that locks it into place (if it's come out, then you can replace it).
Sometimes its held in place by friction (because it might be meant to be removable - I have one that's convertible from an oblique to a straight holder); if that's the case, you can try bending the folded metal part that slides into the slot so that it's open a little wider and will provide a bit more tension.
Sometimes it's glued in, and the glue has failed. You can brush a little sac shellac or wheat glue onto it and stick it back in.
--best wishes with the adjustments! K