Begin by moving your table down enough to accommodate the barrel.
Because this is an irregularly-shaped item, we'll use the center-center engraving feature. To do this, place the barrel anywhere on the table, disable your X/Y axis and move the laser head to the area you want to engrave. Press the "Set Home" button, and this will be your new home position.
If you want to ensure the pattern engraves in your desired location, draw a vector circle around the design and send ONLY that job to the laser with the lid open. Run it with the red dot pointer on and you'll see exactly where the engraving will end up.