@MuhammadNaufalIhsan ,
Note: Exercise extreme caution when connecting to Portal's PostgreSQL database
1. Open command prompt
2. Change the directory to portal's PostgreSQL bin directory. Ex:
c:\arcgisportal\pgsql_14.5\bin
3. Connect using the initial Portal Administrator username/password when portal was installed:
If you do not know the username/password, this can be updated through Portal Administrator Directory > System > Database: