You can write-click, in pgadmin4, the table, click Properties, go to Constraints tab, showing you the Primary Key info, and there you'll see the constraint name (by default tableName_pkey), and the columns. Then, you can, if you wish, click delete and then you can make a new constraint, putting the columns that you wish. It's good to take a screenshot of the constraint, before you delete it, so you can refer to your screenshot, while you make a new constraint.