@minhthu215, Vietnam is a supported Viveport region. Developers on Viveport have complete control over which regions and countries their content is distributed in so you'll see some variation on which titles will be accessible in your specific region.
To reach Viveport's customer service team, email firstname.lastname@example.org
To connect with a live support agent for hardware support, go to www.vive.com/support, click on "contact us" in the top righthand corner, and then opt to speak with a Live Chat agent David R
Technical Specialist - San Francisco, CA; Monday-Friday