The hardest part is unlocking the dungeon Fangbreaker Island. And "hard" only means time consuming.
How to unlock this dungeon: It needs to be unlocked in the Storm Kings Thunder Campaign. It requires some previous steps and I found the Bryn Shandar Reputation to be the rarest material.
When you start the campaign you will first have to do some story missions to unlock all the maps within this campaign. This shouldn't be to much of a problem. Then it comes down to check in daily or at least every 3 days to do some of the repeatable missions. There is 1 mission that gives Bryn Shandar Reputation each on Lonelywood, Cold Run and Bryn Shandar itself. I would prioritize these and do as much of the other missions as your time allows. Especially on Lonelywood there are a couple of other achievements you will get along the way.
As of May 2020 all the maps are still somewhat crowded so you shouldn't have a problem finding other people to help you, if you need.
For the Fangbreaker dungeon itself: it is listed under Epic Dungeons (though it does not count for the achievement for completing 25 epic dungeons, same as many other DLC epic dungeons) and the requirement is an item level of 15,000.
Once you have it unlocked and meet the item level just queue up and wait. Took me around 20 min to find a match and another 15-20 min for finishing the dungeon.
Even if you are on a low level character there will most likely be some (very) high levels in your group that will make this a breeze. It is a run-dungeon, compared to other arena-dungeons so at least do you best and stick with the group.
If you have problem with meeting the item level: the Undermountain campaign is currently basically throwing decent gear at you (800-900 IL pieces in random drops and for story quests). You can also buy 850+ gear for VERY low Astral Diamonds in the auction house. Like 1,000 AD per piece.
Additionally take care of you companion, your mount, your enchantments and 15,000 shouldn't be a problem.