PLS-00103: Encountered the symbol "ALTER"

Hi,

On 19c on AIX

This is my code:

BEGIN

IF $$ORACLE_SID="myCDB" THEN

alter session set container="myPDB";

END IF;

END;

And I receive:

alter session set container="myPDB";

*

ERROR at line 4:

ORA-06550: line 4, column 1:

PLS-00103: Encountered the symbol "ALTER" when expecting one of the following:

( begin case declare exit for goto if loop mod null pragma

Thanks.