There is no more 1040-EZ or 1040-A starting in 2018. Only 1040 and that's it.
With the online version, one account, one return. Period. If you start a 2nd return in the same online account you *WILL* permanently and forever overwrite and delete the first return with no possibility of recovery.
To create another account for another online return, simply log out of the account ou are in *right* *now* and then click the "Create Account" link under the password entry field.