Hello JaneRoss-Russell,
Thank you for reaching out Surface Community. You can use tweezer to remove the broken nib or pen tip. Please take it slow in removing the tip to avoid damages on your Surface Pen as it will void the warranty. It would be best as well if you can visit any Local Microsoft Store if there is one near you. I would also like to let you know that pen tip is not part of the warranty because the Service center doesn't have stocks for a standalone pen tip replacement, the same way with batteries. At the moment, pen tips are only available directly from our physical store or online store by purchasing a pen tip kit. Please take note this is only compatible with Surface Pen with single side button.
Regards,
KarenJune_F