Pokémon Dens are all over the Wild Area in Pokémon Sword and Shield. You can get more Dynamax Pokémon to spawn by using wishing pieces at dormant dens, which you can purchase from Watt Trainers, who are in black-and-white uniforms. But you can reset the dens in the Wild Area.
To reset the dens in the Wild Area, you need to complete all of them. You may need to travel around the Wild Area, double-checking every den available for you to find. You’ll need to visit every Wild Area segment and ensure they’re all completed.
After you finish the last den, look around, and you’re going to see multiple red lights all over again. You can resume progress on the dens, and engage them once more.
Anytime you’re having trouble locating an active den in the Wild Area, spend time going to locations you barely frequent. You can do this to acquire new Dynamax Pokémon regularly. If you do not have access to certain areas in the Wild Area yet, don’t worry about them. None of the Pokémon dens spawn over there until you have access to them.