You probably have to place the back of the nib on a flat surface at a slight angle and carefully put some pressure so that the nib bends back and the tines move closer to each other. Unfortunately it's not going to cure your nib for long.
I fear that the shape of this nib and the material it is made of are not very compatible, so it is too soft and will spring even as you write.
Something similar happens to my Conklin Symetric #5 nib.
The pen is rather nice, but the nib is just a lousy piece of soft metal, which bends as I write until it hard starts and then eventually stops writing completely! very frustrating, I have stopped using the pen, until I find a replacement nib (not Conklin).
I assume any # 5 should fit, I plan to get a Jowo or Bock and swap it in, I am not quite sure if Conklin nibs are screw on or friction fit though, have not tried yet.