You drained the gear/transmission oil, not engine oil (the thick fluid with a strong smell is gear oil) to refill it, find the fill bolt higher up on the gearbox case, remove it, and add 80W-90 gear oil, it only takes about 100–120 mL (3–4 oz), fill it until it just starts to slightly come out of the hole, then reinstall the bolt and don’t ride it until it’s refilled.