In the ultimate auction, once the auction has expired, the admin can not change the end date of that auction product.
The reason is that we save auction status in the Database And if the auction end date is editable then we will have to change the auction status too which becomes complex and is not advisable.
And that is why we have disabled editing of the end date.
If you have any custom requirements for changing the ending date, you can share them with us.
If you want to change the end date, you can change it before the auction expires.
Thus, the PRO version has a relist feature that will relist the auction and the logic has been handled properly in terms of auction status.
In the ultimate auction PRO version, once the auctions expire, you can relist any auction product as per your requirements.
You can also test the PRO version demo here.
Take a look and after that, if you will have any questions, do let us know.
Thank You