Position Spreadsheet Update Won't Sync Assignment

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Hi all.

I'm required to update all the positions in my organisation. I do it using the spreadsheet, however I noticed that the changes I do to the positions won't sync to the relevant employee's assignments.
I have turned on the Position Syncronization Configuration under Manage Enterprise HCM Information. It won't sync if I mass upload the position using a spreadsheet.

Can there be an easy way to do so or I have to update the assignment separately?

Thanks.
Ben.