If you don’t see any insects on the leaves or the soil, I’d just give it some time. Water it every 2-4 weeks. If it’s a large pot of soil do it every 4 weeks with ~0,5 liters, in a smaller pot do it more often with a smaller quantity.

In general, it’s better to water rarely, so the top layer of soil is dry most of the time. That way, you’re making the life harder for small flys to lay eggs and nurish from the roots.

If it keeps losing leaves, don’t panic. Mine had a severe sunburn once and dropped all the leaves. After some weeks it started to recover and grew new leaves.

I would say, the worst thing you can do is overwater. Mine is in a pretty huge pot (80 liters) and I give it (round about) 1,7 liters of water every 6 weeks in summer and 2-3 months in winter. That way the plant has to grow deep roots to the very bottom to reach the bottom and the top layers are rather dry.