If you want to update vouchers date without opening it one by one, you need to follow these steps:
Step 1: Take backup of your company.
Step 2: Open your company then go to administration.
Step 3: Select Bulk Updations and click on bulk voucher creation / modification.
Step 4: Select the voucher type such as sales, purchase, etc then click on configure button.
Step 5: Here, you need to add format and configure all the fields used in the voucher.
Step 6: Now, select the format you have created and press F2 and you will see every field columns.
Step 7: Here you will see date column in that you can update the date as required then save.