Complex sentence: If an accident happens you will be sent back to the start page to ask for a "second chance" in which case you will be sent back in time so, hopefully, you can avoid making the accident a second time.
Split into simpler sentences: If an accident occurs, you will be sent back to the start page to ask for a "second chance". You will be sent back in time so that, hopefully, you can avoid making the mistake a second time.