Access to SQL Syntax (Update query)

Trying to convert Access syntax to SQL (Update Query)

UPDATE dbo.tbl_DriveSalesSidhilMatrix
Set tbl_DriveSalesSidhilMatrix.EnteredBy = case when OperatorName is null then Operator else OperatorName
From dbo.view_Z_SalesOrderAmmendmentsSums INNER JOIN
                         dbo.tbl_DriveSalesSidhilMatrix ON dbo.view_Z_SalesOrderAmmendmentsSums.Operator = dbo.tbl_DriveSalesSidhilMatrix.EnteredBy LEFT OUTER JOIN
                         dbo.tbl_Syspro_Operators ON dbo.view_Z_SalesOrderAmmendmentsSums.Operator = dbo.tbl_Syspro_Operators.OperatorCode
WHERE (dbo.tbl_DriveSalesSidhilMatrix.RecordSource = N'Sidhil')

I'm getting "Incorrect syntax near the keyword 'From'."

Can anyone help?