Laying on your stomach can sometimes help relieve gas buildup in your stomach depending on how much gas buildup is trapped in your stomach.
Sometimes laying on my stomach when I have gas buildup helps to get rid of the trapped gas in my stomach and other times it doesn't.
If I have just a little bit of gas buildup in my stomach then laying on my stomach for an hour or so usually gets rid of the gas trapped in my stomach and then fart it out and I feel better.
Other times I have to lay on my side to get rid of the gas buildup.
So if laying on your stomach doesn't work to get rid of the gas buildup then try laying on your side.
Laying on either side usually works most times for getting rid of trapped gas in your stomach.
On a bed, sofa, or the floor, lay on your side and gently draw both of your knees toward your chest and within a few minutes or so the gas should escape.
If you don't get relief from the gas buildup in your stomach after several minutes, try slowly moving your legs down and up a few times.