With all the Pokemon Gyms now saved from Dynamaxed Pokemon, you will gain access to the Energy Plant within Hammerlocke. You will find either Sordward or Shielbert (depending on your version) there with a number of fans, and he'll once again Attack Sonia's Research and insist that their ancestors were the true saviors of The Galar Region on the Darkest Day. The two brothers intend to use the Dynamax Energy to show that Zacian & Zamazenta were not the true heroes.
As their brother is dealing with Zacian/Zamazenta upstairs, you will have to defeat the other in battle before gaining access to pass. If you're playing Pokemon Sword, you will again battle Sordward. If you're playing Pokemon Shield, you will battle Shielbert once more.
Pokemon Trainer Sordward: Level 64 Sirfetch'd, Level 64 Golisopod, Level 64 Doublade, Level 64 Bisharp
Pokemon Trainer Shielbert: Level 64 Sirfetch'd, Level 64 Bronzong, Level 64 Falinks, Level 64 Klinklang