Short answer: Open the Launch menu at the top right of Forge and choose Preview. Your game opens in a clean run from the very beginning - exactly the way a reader starts it - in its own throwaway save slot, so your editing position and story state are untouched. When you're done, press Esc to return to editing right where you left off.
Where Preview lives
The Launch menu is the control at the far right of Forge's top bar. It holds three actions, from private to public: Preview (a run just for you), Share (a playable link for others), and Publish (submit your game). This article covers Preview.
What Preview does
Preview always starts a fresh run from your story's true beginning - the same first moment a brand-new reader gets, with no variables, choices, or progress carried over from your editing session. It plays in its own throwaway save slot, so it never touches your own saves, and closing it drops you back into Forge exactly where you were editing.
Every press of Preview starts over from the beginning. It's the front-door experience, not a resume.
Preview vs playing on the Stage
The Stage is your live working view: the playhead sits wherever you're editing, often mid-scene, with whatever variables your session has accumulated, and clicking timeline events moves you around freely. Preview is the opposite - the reader's front door. Use the Stage to check a moment while you edit it; use Preview when you want to feel the real first-time experience end to end.
Getting back to editing
Press Esc to leave Preview and return to editing. Your playhead, selection, and story state in Forge are exactly as you left them.
Your playback settings don't follow to readers
The playback preferences in Forge's settings (the gear) - audio volumes, text-reveal sounds, text size, auto-advance, captions, and so on - shape only your own experience while working on the Stage. Preview keeps its own separate set of playback preferences, adjustable from the in-player settings while previewing. None of these ever change what readers get: reader-facing defaults live on your project's Settings page outside Forge.