How to grant the database owner (DBO) the EXTERNAL ACCESS ASSEMBLY permission?

This worked for me:

EXEC sp_changedbowner 'sa'
ALTER DATABASE [dbase] SET trustworthy ON

and I also did this:

sp_configure 'show advanced options', 1;
GO
RECONFIGURE;
GO

sp_configure 'clr enabled', 1;
GO
RECONFIGURE;
GO

sp_configure 'show advanced options', 0;
GO
RECONFIGURE;
GO