alter authorization in SQL Server

Question

I will to made a database diagram in my SQL Server Management Studio. But I have this warning that said:

Database diagram support objects cannot be installed because this database does not have a valid owner. To continue, first use the Files page of the Database Properties dialog box or the ALTER AUTHORIZATION statement to set the database owner to a valid login, then add the database diagram support objects.

Can you help me whit this error? How can I give myself (hein_) the promision to continue?

@JeffersonBElias suggested me to execute this code:

select suser_sname(owner_sid) as usersname from sys.databases where name = 'FreeTimeDBSSA'

What me gives this:

+-----+-----------------------+
|     |       usersname       |
+-----+-----------------------+
|  1  | DESKTOP-3BMCMPC\hein_ |
+-----+-----------------------+

Here you have my Object Explorer:

Answer 1

I have found it whit a hint from @JeffersonB.Elias. I've execute this code:

ALTER AUTHORIZATION ON DATABASE::FreeTimeDBSSA TO sa;
GO