Is there a way to rebattle trainers?

[Mr. Burtrono]

I didn't know about the H patch until a few hours in. Is there any way to rebattle previous trainers to unlock their entry in the dex or do I need to start over?

[Ovrlord Etna]

I was like 3 hours in, restarted myself. Its a quick game I unlocked everything in 20 hours.