Re: How to go back and do the explorer quest you have past

I am not sure what you are talking about

There are 

1. Main Quests - have to be done, sooner or later, have to be done in order

2. Discovery Quests - optional, you can only do one at a time but in any order you want

3. Event Quests - Time limited quests that have to be done between certain dates

the spa quest you mentioned is an Event quest, as the only spa I know of was from a time limited Live Event

Both Main quests and Discovery quest have timers to earn time limited prizes but you can finish them in your own time, you just loose the time limited prize

Main Quests and Discovery quests can not be re-done, once they've started you do not get a second chance of doing them over

Most Discovery quests starts by talking to someone in the park

Here's a list of Main and Discovery Quests