While "online" conversion is possible by treating the XAPK as a zip file, the most reliable way to is to do it locally. By extracting the file manually or using a dedicated mobile installer, you ensure that the OBB data remains linked to the APK, saving you from "Resources not found" errors.
the extracted folder to find the base APK file and an Android folder containing the OBB data. Method 2: Using a Third-Party Installer online convert xapk to apk repack