The Page Settings screen sets paper size & controls the placement of the grid on the page.
First, open the paper in GridMaker or QuiltPaper.
See the thin black outline around the grid? The black line outlines the size of the paper.
Now, tap the Page Settings icon in the side menu (the rectangle 2nd to last) and notice a blue dotted-line instantly appears around the grid. This blue line outlines the margins.
To move the grid location on the page --adjust the page margins by tapping the +/- buttons. You'll see the blue lines moving in or out as the grid repositions itself from its default placement (anchored to the lower left corner) to where you'd like.
NOTE: Adjusting margins also gives you a bit more control over the grid itself:
Add more rows & columns to a grid by reducing margins
Reduce number of grid rows & columns to a grid by increasing margins