A module (elastic) has come off
The wire of your brace is held in by elastics which can be grey, clear or coloured. The coloured modules give a brace a coloured appearance.
A single lost module does not require you to come back any earlier. Multiple lost modules may make the wire very loose and the brace inefficient.
If you manage to recover a module, you can try to put it back on using an opened paper clip or a pair of tweezers. This can be a bit of a fiddle but with some patience, it might just work!
The elastic will fit on each of the 4 corners of the bracket. If you can only get it on 2 or 3 of the corners, that is fine.
If more than one module is off, contact the practice for an earlier appointment.