I want to override a potentially infected website

There is a website that I believe is safe but a vast is not letting me open it. How do I override this? Thank you.

Have you checked the site url on Virus Total to confirm it is clean and safe?
If clean you can submit a false-positive form to avast for consideration. See: Choose Your Sample Submission Type | Avast

You could add an exception to avast webshield, but that would be at your own risk.