He doesn't have any clue specifically. Pretty sure it was Paul who told him that this was a region he hadn't searched at all. So it's a matter of covering as much land as possible.
Roxy found Rudy and Zenith's location from Kishirika (when she reached her home in demon kingdom) but I don't know where that fits in the timeline with Rudy right now.
I just don't remember if that was a flash forward or concurrent with Eudy reaching Fittoa. Like there's a scene with Fitz that was definitely a scene from further this season.