The good news: You don't have to!
OrbitKit has smart algorithms which inspect your artwork and place it tastefully in the print area of each product - big and centered. You should not need to manually adjust anything.
If you are unsatisfied with the results, or are looking for some sort of special behavior, reach out to support. We can always make the algorithms smarter!
Two things you might want to know:
The mockup you see when looking at an exhibit on orbitkit.com is a rough approximation rendered quickly in the browser. Size and position may not be accurate. Real mockups are higher quality and use the exact same smart positioning logic that prints the apparel, so always look at the published versions!
You can take over positioning. If your artwork conforms to the Amazon Merch format (4500x5400 pixels), we disable the automatic positioning code for most apparel. Your artwork will be used as-is, with spacing determined by your transparent borders (just like Merch). Note that this only applies to products with tall/narrow print areas; hoodie fronts are adjusted to landscape orientation (if possible).