Most HTC phones are able to detect which mobile operator you're using based on the SIM card you inserted, and then use the preset Access Point Name (APN) to connect to your mobile operator's data network.
You can add a new (APN) when roaming or if you have difficulty establishing a data connection.
With two fingers, swipe down from the status bar to open
Mobile data is off, tap the
Mobile data tile to turn it on.
Tap to open the
Mobile network settings screen.
Access point names.
APNs screen, tap
and enter the APN settings.
and then select the new APN on the
Some mobile operators may not allow you to change the predefined APN or add new ones.