The game’s Training Room feature is a good framework for helping players learn the game. Instead of nerfing the current content, make some unique categories in the training room for each guardian/abyss dungeon.
Soul Calibur does this decently.
It can summon one boss at the center of the room, that only performs one attack/mechanic at a time over and over, and you can try to dodge/counterattack/stagger whatever the answer is 3 times in a row before accepting to learn the next one. If you fail it, you can just try again respawning on the spot so it’s not demoralizing for bad players in front of a group.
The next lesson can be the same boss, doing a different move/mechanic and so on. All with dialogue and icons describing the dangers, highlighting relevant skills or suggesting battle items like stagger bombs.
The last lesson can be the boss doing all of the mechanics in a row in that low risk easy to learn environment, and maybe upon successful completion award you a title saying “Tytalos Expert” or “Hildebrant Castle Student” or something. Adding some honing materials, cosmetics, or gold to first time completion will help incentivize all players to give this training a try.