This can be solved by setting the sequence number (MxSheet.Sequence) in the sheet settings correctly.
When a sheet is created, all sequence numbers are set to the default value of 1.
Also, in the edit screen (MxSheet_NewEdit), the Sequence item is not editable, so it cannot be changed.
Please change the screen so that you can edit it, and try to set the sequence number according to the existing Excel sheet order.
Have you seen following relevant posts on this topic. Maybe it helps.
Still I can't do it while uploading existing excel file. Does anyone have an idea to solve this issue?