Depends on which version of nipple it has.
If it's the newest adjustable 510 (that was available in 2015) the bottom piece of the nipple just needs to be
threaded back on and tightened. Look to see if the piece in the tube has
threads. Using the tube to screw it back on makes it easier, then snug it down fairly tight.
On earlier nipples the bottom portion of them could break off and you would have to replace the entire nipple new. Reosmods should have replacement parts. You could also send it in for repair, or have it updated by Eric.
Here's a video Russ did back then that shows how to replace the old style nipple if that's what you have. The nipple fix starts at 9:15 in the video.