https://wccftech.com/esim-support-coming-with-ios-12-1-but-you-cant-enable-it-right-away/

At Apple’s Gather Round event, it was announced that the new iPhone XS and XS Max are equipped with eSIM support. Dual-SIM will enable the second line in the iPhone XS and iPhone XS Max. Now, it has been found that eSIM settings are enabled in iOS 12.1 beta 1 which will allow users to use two lines in the same phone. However, you cannot simply make use of the functionality right away. Instead, you will first have to scan a QR code or any other additional information from your carrier. Let’s see some more details on the matter.

Once you have iOS 12.1 beta 1 installed on your iPhone XS or iPhone XS Max, the eSIM settings can be accessed from Settings > Cellular. You will be presented with the required options to enable eSIM support. You will see carrier details for your current line which are assigned to the removable nano-SIM. Below this option, you will find a new Add Cellular Plan option. Once you opt-in, you will be asked to scan a QR code provided by the carrier. The code will contain all the necessary details to activate the line.