SKULabs automatically attempts to link known shipping methods to the requested method but we're very conservative to not mistakenly link a requested method like Express AM to Express.
Where SKULabs does not automatically choose a method we have a few ways to set the shipping method on orders:
Shipping method links are links between your store's shipping methods like "Ultra Saver Shipping" being mapped to "Least Expensive" or "FedEx® Ground (2-3 Days)" to "FedEx - Ground".
Go to Settings page > Shipping tab > Shipping method links
Click on Create new shipping method link, and in the screen that appears, select the store, the requested method and the shipping method to use
Click save
You can permanently hide or show specific rates like Media Mail and Library Mail on the enabled methods page.
If you want to use rules to select a specific method using more criteria than an exact match of the requested method, shipping rules can be configured to set a default for a wide variety of criteria such as specific SKUs, order value, or number of items.
Finally, on your store settings pages you can set a default shipping method per-store which is the least important of the settings and will be overrode by any others settings.