You can link a product to related products if you have the related products Product ID, Model, SKU, or UPC inside your feed. This will only link products that exist in your store prior to the import, not new products that only exist in your feed and not your store.
For linking multiple related products to one product, you may select a delimiter to separate each value. Here is an example of how it could look in your XML or CSV feed:
XML (inside your product tag):
In Step 2, you will need to select what the matching value of your related products is. In the example above, we select "Model". For the delimiter, we enter ":".
In Step 4, we map the market column/tag to the Related Products field.
When the import is complete, the related products will be mapped to the product under the Links tab:
Working Around Pre-existing Products in the Store:
If you are confused about how your products need to be pre-existing in the store before you can Map an existing product to them then there are two ways around this below:
Firstly: (the more difficult way) what can happen with this setting is that the feed can be thought of as being in logical order, so you can have products at the top of the feed be related to products at the bottom of the feed. Products will be added to the store as Total Import Pro works it's way through the feed then the products at the bottom of the feed can be related to products at the front of the feed.
Secondly: This way is simpler but requires two imports. What you can do is complete your first import without Mapping the Related products field, then do another import where you have the related products field Mapped. In the second Import all your related products will be updated.