Does a relationship have a single contact person with whom you maintain communication, or are there multiple contact persons applicable for this company?
Then you can add them to the company under the 'Contact persons at this company' tab. If you haven't created this person in Simplicate yet, you can do so by adding a new person on this page.
Click on 'new'
Choose an existing person or create a new person via this pop-up
Enter the job title, email address, and phone number
Check whether this person is eligible for any created interest
