What do I need to do with the same client domain. For example, DomainA.com and DomainA.vn.

What do I need to do with the same client domain. For example, DomainA.com and DomainA.vn.
What can I do to not have to delete 1 of 2 ? And if I have to delete, what should I do to best? Please help me

if they have the same content, or if you want to keep them both you can 301 redirect one of the them to the other... or maybe forward it, I'm not sure which one