You can change the season on a Sales Order unless subdocuments have been created or their quantities are linked to dockets.
If subdocuments are present, inactivating them will not unlock the season field. In that case, the required workaround is to copy the order, set the correct season on the new copy, and then inactivate the original order.
Warning: The 'Change Order Season' field needs to be been permitted in your document settings.
If you are unable to complete this task, you or your system administrator will need to amend your User Permissions and Company Settings.