Download & Install: Install the Sales Backdate and Postdate in Odoo from the Odoo App Store.

Navigate to the Sales module, then go to Configuration >> Settings.
Scroll down to the Sale Order Backdate section.
Enable the primary feature by checking the Sale Order Backdate Feature box.

Once enabled, the following options will appear. Configure them to fit your workflow: Add Custom Remarks to Sale Orders, Set Invoice Date Same as Order Date, Set Delivery Date Same as Order Date

When enable Add Custom Remarks to Sale Orders, then the Mandatory Remarks on Sale Order field will appear.

For Bulk Updates: To allow a user to backdate multiple orders, navigate to
Settings >> Users & Companies >> Users.

Select the user, and under theTechnical access rights, check the box for Multiple Assign Sale Backdate.

To Backdate a Single Sales Order:

Navigate to the Sales module and open or create a quotation.

Click the Quotation Date field and select your desired past or future date from the calendar.

Fill in the Remarks field if it appears and has been made mandatory in the settings.

Click Confirm. The date you chose is now the official Order Date.

Use the smart buttons to check the corresponding Delivery and Invoice.
The Scheduled Date and Invoice Date will now match the new Order Date (if you have enabled this in the settings).

To Backdate Multiple Sales Orders at Once:

Go to the main quotation list view by navigating to
Sales >> Orders >> Quotations.

Select the checkboxes next to all the quotations you wish to update.
Click the Action button at the top of the list.
Choose the Multiple assign backdate option from the menu.

In the pop-up window that appears, set the new date and add any remarks. if you want to Update invoice dates or Delivery dates, then Tick the corresponding boxes, After Click confirm to apply these changes to all selected orders.