Every Hatch pattern has its origin point and when you apply a Hatch in an area inside your drawing, AutoCAD selects the origin point for it. But if you want to specify an origin and want to force AutoCAD to select your preferred point as the origin, then you can use the Set Origin option from the Origin panel of the Hatch Creation tab, as shown here:

In the following screenshot, in A, the Hatch pattern has been applied normally without selecting the origin, whereas in B, the same pattern has been applied with the origin selected as the lower-left corner of the rectangle:

As you will notice in A, the brick pattern that starts at the lower-left corner of the rectangle is smaller than a full block because the Hatch did not start from there, whereas in B, the lower-left corner brick marked with the red circle is a full block because the origin of the Hatch pattern is that point.

To set the origin, start the Hatch command, then select the area where you want to apply the Hatch. Then, click on the Set Origin tool from the Origin panel of the Hatch Creation tab, and click at the point that you want to specify as the origin. After specifying the origin, the Hatch will automatically adjust so that the pattern starts from the selected origin.