We can definitely create relationships manually. Any user with create permission can add a Relationship to an Account from the Customer 360 > Relationships section.
Steps to Follow :
- For a specific customer that you’d like to map to a relationship type, navigate to the Customer 360 Details view > Relationships section.
- Click Add to add the desired Relationship.
- Select the Relationship Type from the drop-down menu.
- Enter/customize the text in the Relationship Name field.
- Then click Save. It will take you to a detailed view of this relationship.
Once the relationship is mapped, then end users can see the Relationships card view in the Customer 360 > Relationships section. Click the Relationship name in the card view to access the Relationship 360 for that particular customer.
For more information, check this link