A simple Anki addon to reset the ease of an entire deck. Tested & working on Anki version 24.04.1

You need to have a "Current Deck" selected. Simply click on the deck you wish to reset. Your current selected deck will be highlighted within Anki.

In the image below, notice how the "Grammar" deck is highlighted.

Then you select Tools > Reset Ease of Current Deck.

Every card within the deck will be reset to the default ease value of 250%.