Hey there,
I am really sorry for the delay of this reply as it is a weekend for us here.
You can override this following language constant translation from backend.
COM_EASYSOCIAL_LOGIN_NO_ACCOUNT="Don't have an account yet?"
COM_EASYSOCIAL_LOGIN_REGISTER_NOW="Register now and start interacting with people from this community today!"
You can refer ou documentation here how to override this language constants translation from backend
https://stackideas.com/docs/easysocial/administrators/languages/creating-language-overrides
Hope this will help.