Well first off you have to add an attachment to the unit I think. I've never made a campaign so I'm not sure if the ! is already integreted into the system or not. If not then just make an attachment and put it onto the unit. For the quest making part read a tutuorial, that will provide you with a lot more information that I could and will familiarize yourself with quests.
But use conditions, if hero (paladin) has items = sword turn on trigger -return-. The trigger return would have something like when (paladin) enters rejoin (quest giver) and your events that would need to happen including a quest change to completed.
Hope that helps.