I removed the top but could see nothing broken but suppose the culprit must be under the drum that's causing the problem. How do I access the problem? When you look inside you can see that the drum is resting at a slight angle as there's an uneven gap between the front and back rims and the drum. Are there some sort of supports under the drum that may be broken?

There are roller supports to keep the drum level. You'll have to move the dryer out and take off the back panel. Depending on space, you might need to disconnect the drum belt and tensioner to gain access.