Creating association between two entities manually/using a microflow

I have uploaded a dataset into an entity I created in my domain model using the excel importer module. I have also created an association which links this entity to another. Essentially it is a user table which contains email addresses, which I would like to link to another table which contains user information but not email addresses. In this way I can display email addresses for users in the table that doesn’t contain them by linking them through the user ID. I can see in the database viewer that the table created by the association in the domain model doesn’t contain any records, so I think I have to create a microflow which associates the items using the user ID. Mendix doesn’t know that when I upload the user table with email addresses, that it is to link that to the other entity that contains user information.  Can anyone direct me to an article/information that would help create the microflow which would create associations based on the User ID and populate the entity that contains associations so that I am able to bring in email addresses into the user info entity? Any help would be much appreciated.
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