Hi,
I'm happy to try and assist.
Send me more details about the type of help you're looking for, about the app, the target market + the current status of the app/business, and I'll be happy to try and help. If I can give you some free advice by email I'll be happy to do so. If you'll need more help we can schedule a call.
As for tool, here's a whole bunch of tools and resources from Steve Blank (the man behind the Lean Strategy): https://steveblank.com/tools-and-blogs-for-entrepreneurs/
Best of luck