To get the VoWiFi feature on Realme X2 Pro, first, you need to update your device to software version A.09. Check for the update by going to the system update. Alternatively, download the software version RMX1931EX_11.A.09 (link, link) and flash it manually, then follow the below steps to enable VoWiFi. To install the software update manually on your device, boot it into Recovery (press Volume Down + Power button after turn off the phone). In recovery, select Language > from phone storage > Select the software package > tap OK to begin the installation. To enable VoWiFi on Realme X2 Pro and other Realme smartphones, follow the below steps. The good news is that Realme will add VoWiFi support to all smartphones, including Realme 1. According to the timeline, the entire device will get the update before April 2020, so check your update regularly.
