Use the verb rekindle when you're trying to get something started again, like a fire or a romance.
If your campfire goes out while you're getting the marshmallows out of your tent, you'll want to rekindle it. Likewise, if you've lost touch with a childhood friend, you might try to rekindle your relationship when you meet again as adults. Re means "again," and kindle means "start a fire," probably from the Old Norse kynda, "to light a fire." Rekindle has been used in the figurative sense from around 1300.