To define a relationship in Power BI Desktop, follow these steps:
Open Power BI Desktop and select the Modeling tab from the ribbon at the top of the screen.
Select Manage Relationships to open the Manage Relationships dialog box.
In the dialog box, select the first table that you want to link to another table. This will be the table on the one side of the relationship.
Select the field in the first table that corresponds to the field in the second table that you want to link to. This is known as the foreign key.
Select the second table that you want to link to. This will be the table on the many side of the relationship.
Select the field in the second table that corresponds to the field in the first table that you selected earlier. This is known as the primary key.
Select the type of relationship that you want to create, such as one to many or many to many.
Click Ok to save the relationship.