Hello @DeborahF282 ,
If you're able to log into the account, you can change the username, main email address, and other details from within the account. If you don't have the account's login credentials, but you do have access to the account's main email address, you can recover the username and reset the password to login.
If you don't have access to the account's login credentials, nor access to the account's main email address, you'll want to call in and request an account ownership transfer through our phone support. Phone support may need to confirm some account details and security aspects, if the system doesn't recognize the information your provide to find the account.
I have used Constant Contact for several years and love it. Tonight, a Sunday evening, I need to create a new account and prepare a simple draft email tonight which should not be a problem. But I do not know the email address the entity will want to use to send the email. I also did not know if I could use a placeholder email address and then change it. This question and the clear answer calmed my panic in about 60 seconds of searching for the answer. Thank you! This is one of the very best communities on the Internet for finding an answer. Much appreciated.