Stock Sync provides an easy way for the mapping field which is the Guided Field Mapping. Guided Field Mapping is known as the dropdown list on the mapping field section. 

How to use Guided Field Mapping:

1. You upload a sample of your feed file to the space provided.

2. The Upload limit is 2.0MB only.

3. If you have a feed file that is way bigger than that, then I suggest you create a new file with only the header since you are trying to map the field.

4. After the upload is done, you should be able to get a dropdown list for all your field mappings.