Sending hugs your direction, titles can be the bane of authors. (readers should feel lucky it’s not “TBD” all the way through...)
More seriously, I’d suggest simply using that “new idea title” temporarily until you figure out what you actually want to do. I typically start with a temporary “working title” until I get a ways into the chapters, when I can refine it later. Maybe the main character’s name, or some other central theme, or a key word/phrase. (ie, for Jefferey, it’s the main character. For Repair Guy, it was a spin on a common trope.)