There is a tutorial for this here: https://forum.inaturalist.org/t/using-the-field-similar-observation-set-for-linking-observations-of-lepidoptera-when-raising-on/1018
Other folks have wanted to do similar things, e.g. https://forum.inaturalist.org/t/connecting-observations-into-linked-groups/1367 or https://forum.inaturalist.org/t/uploading-observations-of-the-same-individual-over-time/2956.