There are a few opposites I can think of. The first is having humility. An entitled person is likely prideful and expects a great deal because they think they are something special. An appropriately humble person will not feel entitled. This aspect focuses on how the person feels about themselves.
Sometimes we will talk about people like this being very down to earth, which emphasizes that their expectations from the world are realistic or modest.
If we are talking about how they interact with other people, we might use a word like unassuming. This emphasizes that their interactions with other people don't convey that they feel entitled. On the contrary, they at least interact with others in a way that conveys respect for them. This is a word about how they behave superficially, they may feel inwardly entitled but they don't show it. It's often used when we expect people to feel entitled because we view them as higher than us, but then they interact in a pleasing, humble way.
You can also say that someone doesn't have or doesn't convey a sense of entitlement.