UploadUserAvatar.swift

private func updateUserRecord(_ userRecord: CKRecord, with avatarURL: URL) {
    userRecord["avatar"] = CKAsset(fileURL: avatarURL)

    CKContainer.default().publicCloudDatabase.save(userRecord) { _, error in
        guard error == nil else {
            // top-notch error handling
            return
        }

        print("Successfully updated user record with new avatar")
    }
}