How do you change the vehiclecostmap to a specific x and y axis dimension. Eg: [0 735] x [0 814] meters to [-30 3] x [-30 1] meters

Hello,

I saved a matlab figure with axis dimension xlim = [-30 3] and ylim=[-30 and 1] as image.png to create occupancy map. The resulting dimension of the image is 734 x 814 pixels. After creating the costmap, the dimension is x_map = [0 735] and y_map= [0 814] meters. The challenge is, how to position the robot's x and y;it must lie within -30 and 3 and -30 and 1 (like originally intended). With my current costmap/occupancymap, how do I normalize/adjust the map dimensions from [0 735] x [0 814] to [-30 3] x [-30 1] . Thank you