How do i turn off downtime on my phone when i don’t know the password?

That is a setting in Screen Time that was enabled by you or someone else, such as a parent or employer. If you don’t know the Screen Time passcode you may be able to recover it if you know the Apple ID and password that were used to set it up→If you forgot your Screen Time passcode - Apple Support

If you don't know it the only way is to restore the phone to factory settings and not restore a backup.

As far as I know, Screen Time and Parental Control restrictions don't set themselves. However, it appears that if you were the one who set the Screen Time passcode, there is a way to reset it using your Apple ID credentials.

Use Screen Time on your iPhone or iPad - Apple Support

Get started with Screen Time on iPhone - Apple Support

If you forgot your Screen Time passcode - Apple Support