Hello Chloe_p_,
Welcome to Apple Support Communities!
We're glad you stopped by and would be happy to help you with Safari automatic logins.
To change one of the automatic logs in Safari follow the steps below to achieve this.
"In the Safari app
on your Mac, use AutoFill settings to fill in contact information, user names and passwords, credit card information, and other forms on webpages.
To change these settings, choose Safari > Settings, then click AutoFill."
More information can be found in this article: Change AutoFill settings in Safari on Mac
Let us know if you have any questions.
Thank you for using Apple Support Communities.
Take care!