Good morning Benson.
If I understand your problem, the front of the flange that you push the nib into, has spread apart slightly, allowing the nib to wiggle a little bit. If that is the case, you can tighten it by squeezing it VERY VERY lightly with a pair of small round nose/needle nose pliers. I would recomend putting something round, like a 1/8 or 3/16 dowel, into the curve on the bottom of the flang. This will prevent the pliers from deforming the flange. You should also cover the jaws of the pliers with a couple of layers of tape to prevent scratching the brass.
With the dowel in place squeeze the front of the flange very lightly, then try your nib. If it is still loose, repeat. If you squeeze a little to hard, don't panic, you can separate it slightly by forcing a nib into it. I use an old nib for this.
If you can, I highly recomend Christopher Yokes nib pliers for doing this work. They are also usefu,l if you decide to get a Zanarian flange, to make your own flanges.
If you have any questions, let me know.
Darrin
https://www.yokepencompany.com/collections/accessories/products/pliers