If you're seeing this, you must have tried to load either a broken or an incompatible save.

In order to reset the game, please google on how to access Local Storage of your browser and delete the save called incremental_fortress1.0

For Chrome, see here: https://developer.chrome.com/docs/devtools/storage/localstorage/

For Firefox, see here: https://firefox-source-docs.mozilla.org/devtools-user/storage_inspector/local_storage_session_storage/index.html