If only your game crashes (not the editor), there must be a bug to report. But first you need to narrow it down, by finding a reliable reproduction. Backup your project, and try to reproduce it in more recent versions of Godot (3.2 beta3 currently).
There are a few known bugs where the game crashes, for example this one: https://github.com/godotengine/godot/issues/20258
Then start tearing it down: remove things not necessary to the reproduction steps. Continue removing stuff until the crash no longer happens, then put back the last thing you removed, and try to remove another.
Once you have the most stripped down reproduction project, you might be able to tell which thing made it crash. If not, you can post a crash report on Github with your test project, and eventually try to debug it yourself: grab the engine's repo, compile it with SCons, and run it with C++ debugger attached to see which line fails.
In the meantime if you want to unblock your project, using version control (Git, SVN...) could help because then you can rollback your recent changes.