When you get to the jail cell with Rowland Oakes inside, he will ask you to go and get his want for him. This want is locked behind a large boiler door that doesn’t have an immediately obvious trigger to unlock. Here is what you need to do to open the boiler door in the Tale of Rowland Oakes quest in Hogwarts Legacy.
If you follow the large metal pipe that is above the boiler door, it will lead you to a large furnace. The wood below the cooking pot will highlight when you get close to it. Use any fire spell to light the fire here. This will start generating steam which will travel across the pipe and open the boiler door for you.