Hi @xylonxx-163 ,welcome to Q&A forum!
Did you delete the SQL server service account by mistake? To change the service account, you could follow the main steps below:
- Add new accounts in the Active Directory Domain Services.
- Configure the service account in SharePoint center administration.
- Change SharePoint Central Administration Account.
- Change the service account in the application pool, services in services.msc and service application.
Please refer to this thread for more details:
Sharepoint 2016 service account change
Reference:
Initial deployment administrative and service accounts in SharePoint Server
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