How do i jailbreak my iphone 7 wth ios 6.4.1 ?

In detail please or send a link. I need it from the very beginning from downloading the cydia impactor and installing it on my pc to successfully jailbreaking my phone

You can't even get iOS 6 on an iPhone 7. The iPhone 7's lowest compatible firmware is iOS 10. You wouldn't be able to downgrade to iOS 10 as the SEP isn't compatible, if you have SHSH2 Blobs for iOS 11.3.1 then you could downgrade to that but by the sounds of it, you don't have that saved.

If it was a typo and you meant 11.4.1 then you can't jailbreak that yet. An exploit for it hasn't been released, anything you find will be fake and potentially dangerous to use.