I need help resetting my iMac I don’t remember my password

Try here.

https://support.apple.com/en-us/HT202860

After you have reset it as noted in the link above, I strongly suggest that you write the new password down somewhere secure. Passwords are very important and sometimes things can happen to them. I keep a spreadsheet on which all my passwords are recorded. I keep it up to date and it is also password protected.