How can I fix it?

The two most common squeeks are the belt and the drum rollers. You could buy abd try belt dressing or squeek ease or just rub bar soap on the belt if it goes around. The rollers are next if it wasn't the belt. Your drum lays in a tray and has several rollers, usually 4. They are usually sealed bears and you can spary them with WD 40 or spray lithium lube. This should give you some peace and quite.

Funny you ask, mine is sqeaking now I write this. I have looked at the belt to make sure it is not loose and it was not. I have not looked at the motor arm to which I am sure the belt must rub against that makes the tub turn and I am not going to... as my dryer is 25 yrs old and I am just going to buy a new one... the average life of a dryer is probably about 10 or 12 yrs and as soon I fix the noise, something else will come up not working. Besides I am beginning to think it's not safe, lots of home fires are caused by faulty dryers... and I am sure it is not as energy efficient as new dryers. You might also ask yourself how old your dryer is...