Find the Linked Activity panel, and relink or unlink it
Open the workout's review page and look for the Linked activity panel. It shows which recorded session was matched to this planned workout, and which of the athlete's connected devices it came from. If the wrong activity got matched, open the relink dialog from that panel. From there you can unlink the mismatched activity, or link the correct one instead. If your athlete recorded the same session on more than one device, the dialog lets you pick the recording you actually want to keep.
An athlete with more than one wearable connected is more likely to run into this. A dedicated view of exactly which devices are connected for a given athlete is coming soon to their profile (see What's coming next). Until then, see Supported devices for the full list of what syncs into Wyder.