Like was said, you can carefully drill out the old piece of blank from the tip top and then LIGHTLY sand the rod tip until it fits.
If that doesn’t work for you, you can use a tip top that is somewhat oversized if you wrap thread around the end of the blank to fill the gap and use 5 minute epoxy or tip top cement to glue the new top on.
You can also use a regular single foot “running” guide instead of a tube type guide and just wrap it on the end of the rod with thread and finish it with epoxy – a number of custom rod builders do this by choice.
New tips are available online at Jann’s Netcraft, or Mudhole. Measure the rod tip with a caliper to get the size and go slightly larger rather than smaller if needed.
Good luck.
Dan