When a plant is overwatered, the color of the leaves starts to change. Look to see if the green is leaving the leaves, turning them pale green or yellow. You may also notice splotches of yellow on the leaves. When the roots are drowning in water, they can’t supply water to the upper parts of the plant. Additionally, the plant can’t get nutrients from the soil. That means it will start to wilt and die. Check to see if your plant is struggling to produce new leaves or stems or has foliage that is dying. Since your plant can also die from not being watered enough, you might feel unsure about whether or not it’s under or overwatered. If you know you’ve been watering the plant but it’s still dying, overwatering is likely the culprit. When there’s too much water in the pot, you may see green algae or fuzzy black or white mold starting to grow on the surface of the soil or on the base of the stem. This is a sign that the plant is being overwatered. You may see tiny spots of mold or algae, or it could be widespread. Any mold or algae is cause for concern. If water sits on the roots for too long, it will start to rot them. When this happens, the roots will give off an odor of decay. Place your nose close to the top layer of the soil and sniff it to see if you detect an odor. It’s possible that you won’t be able to smell root rot if it’s just started or if your soil is very deep. If your pot doesn’t have holes at the bottom to allow for drainage, it’s likely that your plant is getting overwatered. That’s because water gets trapped at the bottom of the pot. It’s best to remove the plant from the pot to check it for root rot. Then, create holes in your pot or transfer the plant to a pot that has holes.  You can create holes in a plastic pot using a knife or screw driver. Use the knife or screwdriver to carefully puncture the bottom of the pot. If your pot is ceramic or clay, it’s best not to try to make holes. You'll likely end up breaking or damaging the pot.

TL;DR in Vietnamese:
Kiểm tra xem lá có màu xanh nhạt hoặc vàng không. Chú ý nếu cây không phát triển hoặc xuất hiện các đốm nâu. Tìm xem có mốc hoặc rêu tại gốc cây hoặc trên mặt đất không. Ngửi xem có mùi khó chịu của mốc không. Kiểm tra các lỗ thoát nước ở đáy chậu cây.