trying to delete data from iphone 6

i no longer have access to the original email that i used to set up my ICloud account. The email address itself is not even valid with the service provider so a password link reset is not going to help me get sign in to that email account.

when i try to delete the data on the iphone, it automatically populates my old email address and prompts me for the password which i don't know.

how do i delete the data on my iphone if the email address is not valid? 😕

thanks!