ADFS 3: Adding second DNS/Domain ADFS server 2012 r2

Currently we have ADFS running on server 2012r2 ... with DNS as adfs.firstdomain.com
Now we have a requirement to add  second domain/DNS to our existing ADFS federation for one application.

For eg: 
App 1 : https://adfs.firstdomain.com/adfs/ls/

App2 2 : https://adfs.Seconddomain.com/adfs/ls/

Please let me know how to achieve this.

Thanks