Start by checking if everyone is safe. Move your car out of traffic if...

https://dlf-ne.org/what-if-the-other-driver-changes-their-story-later-a-paralegals-guide-to-protecting-your-claim/

Start by checking if everyone is safe. Move your car out of traffic if possible. Always get a medical checkup immediately, even if you feel fine. Call the police to get an official report. Take photos of the scene and grab contact info from witnesses