Solved. Thanks everyone.

bool tap_hold(keyrecord_t *record, char *tap, char *hold) {
    if (record->tap.count && record->event.pressed) {
        SEND_STRING(tap);
    } else if (record->event.pressed) {
        SEND_STRING(hold);
    }
    return false;
}

bool process_record_user(uint16_t keycode, keyrecord_t *record) {
    switch (keycode) {
        case LT(BASE, KC_X):
            return tap_hold(record, "zv", "ZV");
        case LT(BASE, KC_Y):
            return tap_hold(record, ",", ", ");
    }
    return true;
}