ServerAlias Apache code please

Hi I am struggling with an installation of multisites using subdomains and having a redirect issue on actual subdomains

I noticed when reading the forum that Apache ServerAlias for wildcard subdomains is sometimes given as
ServerAlias mydomain.com*mydomain.com or
ServerAlias *mydomain.com

Would someone have the actual block of code that needs to be added to the Apache file

Thanks
Brad