Plex will automatically do that for all episodes added within 1 day IIRC:
Adding a single episode will display that episode itself
Adding multiple episodes or an entire season will display that season
Adding episodes from multiple seasons, multiple entire seasons or the full show will display the show
There’s an existing feature suggestion to generally collapse/group episodes by their seasons as well as one asking to only display the show’s poster. I recommend you comment/vote in those threads in order to avoid distracting votes/attention.
