Advice for Adenium care/watering?

A good friend of mine moved and he gave me his desert rose Adenium desert rose, the problem I dont know how to water it.

I have a lot of cacti and also a dorstenia so I know how to water desert plants but this one is confusing.

He got it as a gift, my geus its 2/3years old its got a good caudex and about 15cm height.

He barely watered it.

I watered it since I got it in March twice.

Once a good watering two lover leaves showed signs of overwatering.

Okay, I waited 3weeks and watered it now barely just maybe like a shot glass worth of water.

Now again I see signs of overwatering.

As I said I got a lot of plants, a lot of cacti and dorstenia and I know how to care for them.

This is just confusing, has anyone please help? Suggestions how to better crae for it?