Collectible Card Game Headquarters

When I changed the theme on Forge on my android device, to whichever theme has Fire in its name, the game completely crashed. Now it crashes every time I start it, right at the end of the finishing startup step. So how I get the game back to it's pristine basic mode?

Delete forge\data\preferences\forge.preferences file and try

How would I do that on an android device?

Using a File Explorer app.