That appears to possibly be a knockoff hexagon (or possibly one of the 1.75mm ones?. The real ones that I have seen don’t have an insert tube like that. You can just buy a new barrel from Itworks3d.com but they appear to be out of stock at the moment https://itworks3d.com/product-category/parts/3d_printer_hotends/
your other option is to glue the tube back in place using a thermal transfer epoxy. Artic silver makes a good one that should work if you aren’t printing nylon with it.
Sorry to hear about this issue with the hotend! It looks like a set screw may have been missed on this hotend that keeps this tube in place. If you can contact us at support@lulzbot.com or fill out our support form here: https://www.lulzbot.com/support we can see about getting a replacement.