The bounce rate is calculated as percentage of number of leads created in last 7 days (by Created Date) VS number of leads bounced (Deactivated -> Bounce Deactivated) in last 7 days (by Modified Date). This is at the Organization level, i.e. across all the assistants in the Organization.

The day, the bounce rate goes below the limit, you can restart the BounceRisk leads. It is highly recommended that you be extra careful in handing these leads. Because again if the bounce rate goes beyond the limit you would be stuck with the Bounce Risk emails for 7 more days.

You can check Bounce Rate by clicking on Org Messages > Org Details.The page will look like the below image.