1. Join a PvE guild
2. Magicka regen is moot in PvE. In PvE, spell damage>max mag>cost reduction is the meta
3. Boss does 3 phases, lightning (blue), Fire (red), Poison (green).
Blue phase:
Adds come out during the blue phase, focus them during blue phase before going back to boss.
Red phase:
If boss is moving towards you - stay on the far side of the mortars.
If boss moving away from you - stay in between the mortar drops and boss.
note: only the initial mortar drop causes damage, then the red circle remains for a second in which you can stand in it without taking damage.
Green phase:
Continue to follow boss but make sure the group stays close together. Healer needs to heal through this phase. big heals.
4. stick with 5 light/1MA/1HA. The fourth LA passive "prodigy" requires a full 5 piece, increases you spell critical, which increases your heals.
5. Work on possibly switching to dps if you can find any. request in zone for helm farm specific runs. A lot of DSC can be skipped. Try to find someone who knows when and where to skip in the dungeon.
Finally, it may be likely that undaunted sets will go to v16 in the next patch...so a lot of us are saving our gold keys. the undaunted chest obv is the only place to get the shoulders.
So first are you PC/Mac or Console?
If you're PC/Mac I would suggest you go to where the undaunted pledges are for your alliance, for instance Mournhold in Deshaan for EP. Ask in Zone for people wanting to grind for this helmet and you should find someone.
As far as the dungeon/battle goes there are a few things in this dungeon you can do if you are specifically interested in just the helm.
You have to fight the ground pound boss and the actual Engine Guardian boss (the final boss) All others can be skipped either by running/sneaking past or letting your group die then run while in "ghost mode" to the next area.
For the final boss forget a tank, it's not necessary or useful to have one. If you have a tank in group try and get them to switch to DPS as much as they can. The boss is a pure ranged DPS fight and you as the healer will be really busy.
The boss goes through phases as you probably saw. A fire phase a poison phase and an electric phase. Just learn the signs and how to react to each but most importantly just do mass DPS on the boss. The only time you shouldn't be hammering the boss is when those dwarven spheres spawn. If you have a DK have him equip chains and pull all of those spheres close and everyone AOE them down quickly then right back on the boss.
Hope that helps.