After a wreck, prioritize safety and call 911 to get an official police report....

https://lima-wiki.win/index.php/What_If_You_Didn%E2%80%99t_Get_Witness_Names%3F_A_Paralegal%E2%80%99s_Guide_to_Reconstructing_Your_Claim

After a wreck, prioritize safety and call 911 to get an official police report. See a doctor immediately, even if you feel fine. Take plenty of photos, collect witness contact info, and watch what you say to insurance adjusters