Oftentimes developers will build things in a testing environment and need transfer their changes to a live environment once they're approved. Conversely, you may want to pull all of your field configurations down to your test store. Normally this task is manual and tedious.
The sync feature to allows you to sync your field configurations easily. This comes in handy if your store features a large variety of different fields.
This feature is only available on the Plus plan.
Log into both of your stores and open Custom Fields for both. Hover over the Settings tab at the bottom of the sidebar and click on Sync Fields.
Here you can select the store that has the field you want to copy, then the Resource Types and specific fields you want to sync.
Easy, right? Now the fields that you selected will appear in the other store. An easy way to check is by clicking the link provided after you Sync.