Need to start from scratch - Migration from Photos

I'm brand new to Lightroom CC. I just migrated all of the photos from Photos on my Mac to Lightroom CC. I haven't touched anything since the migration, but there are still tons of duplicates that were copied over from Photos. I evidently missed the option to have Lightroom check for duplicates upon migration.

1. How do I delete everything I migrated from all aspects of Lightroom (cloud and local) so that I can try again from scratch?

2. Is there a better way to do this? I have about 50,000+ photos so manually checking for duplicates is not an option.

3. On a related note, is Lightroom Classic better for finding and deleting duplicates?

Thanks for your advice.