Short answer
HubSpot's KB: Reject all removes suggested pairs from the potential duplicates table and from future scans. To cut noise first, use Refine suggestions to compare extra properties; pairs with different values for those properties are filtered out. You need Data quality tools access and Edit set to All contacts or All companies.
1. In HubSpot
The relevant screen in my demo portal.

2. Worth knowing
Run Refine suggestions before Reject all, so you only clear the pairs you've checked.
3. Related
The duplicates tool and duplicates after an import.