Here’s a tutorial you can link to as a way to help observers fix this issue: https://forum.inaturalist.org/t/how-to-fix-your-observation-with-photos-of-multiple-species/15096
In the comments on that post is also some boilerplate text I use for observations of this sort.
And here’s a feature suggestion that might allow this type of observation to be improved even if the original observer doesn’t return to iNat: https://forum.inaturalist.org/t/easy-way-to-mark-multiple-species-observations/278/54?u=rupertclayton