Wacom Intuos Pro Manual page 30

1. To replace the pen nib, use the nib removal tool to grab the old nib and pull it straight out of the pen.
2. Get a replacement nib and slide the end of the new nib straight into the barrel of the pen.
3. Push the nib in slowly and firmly until it stops.
If you need pen nibs or other accessories, go to the Wacom Store.