You want to add a soft credit to a constituent without creating a relationship between the donor/main constituent and the constituent you are soft crediting.  

In version 4.7 and after, you can add a soft credit without adding a relationship if the constituent that is to be soft creditted is already a Constituent and you have their Import ID.  To do this, rather than select the mapping for a secondary constituent in the Soft Credit mapping, you will need to link to the Import ID.  This may mean that you will need to add that field to your file or that you will need to use Data Transformations in order to map that data correctly.

You can read more about mapping soft credits in this section of our User Guide.

In versions prior to 4.7, you will need to:
  • Create an Individual mapping for the constituent you wish to soft credit. 
  • Run the import but on the review screen change the relationship action to 'ignore'. 
When you run the import and commit the batch the record will be updated with the soft credit but the relationship won't be added.