* Access the Transfer Tool:
* In the Google Workspace Admin console, navigate to "Users" > "Transfer tool for unmanaged users".
* Identify Conflict Accounts:
* Use the tool to search for unmanaged users (conflict accounts) that have email addresses matching your company domain.
* Send Transfer Requests:
* Send transfer requests to the identified unmanaged users, asking them to transfer their accounts to your Google Workspace domain.
* Complete the Transfer:
* Guide the users through the transfer process to ensure their accounts are moved to the managed Google Workspace environment.
* Verify the transfer completion and resolve any remaining conflicts.
References
* Google Workspace Admin Help: Transfer tool for unmanaged users

You can use limits with Google Cloud Directory Sync (GCDS) to set the maximum number of deletions permitted on each simulation or synchronization. If it reaches this limit, GCDS stops and does not sync any changes. https://support.google.com/a/answer/9520714?fl=1