If your tire's air pressure is too low, the first thing you should do is refill it with some air. Re-inflating it won't just ensure that your tires aren't undergoing excess strain, but it's better for your car's performance, and allow you to grip more securely onto the road. The latter is crucial for your safety. However, if your tire pressure keeps dropping afterward, you might need to consider visiting a tire shop. If your tires are too old, they can introduce small leaks that let the air out. In this case, you should consider replacing your old tires. Or, it might be leaking air due to a puncture, which can be repaired depending on how severe the damage is. Otherwise, your wheels/rims might be bent, in which case they too could be repaired, if the damage isn't too bad.