Implicit sharing is automatic. You can neither turn it off, nor turn it on. It is native to the Salesforce Platform. In other words, this isn’t a configurable setting available in Salesforce.
To remove User’s implicit access to the account, you have to remove his/her access to Opportunities, Cases, or Contacts under it. Develop a batch to take care of this.
Using Mass Transfer records will allow transferring Accounts, Opportunities, Contacts and Cases.
1. Go to Mass Transfer Records.
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2. Click Transfer Accounts.
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3. Select the appropriate options.
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