1. Check if you had installed the ODBC driver for PostgreSQL if not, please perform the following steps from this article: 
Configure ODBC drivers for PostgreSQL.
2. Then, after checking/installing, please open TestStand.
3. Select 
Configure - Result Processing
4. From the pop-up window, select database 
Options
5. In the new window, select 
Build
6. Go to 
Provider, select 
OLE DB Provider for Microsoft Directory Services, and click 
Next
7. Here you must fill in the following fields
- Data Source (Please go to this * step )
 - Location (location of your system)
 - User Name
 - Password
 
8. When complete, please Test Connection and click 
OK if everything works.   
  9. Then copy 
Connection String Expression to the Property Loader 
SOURCE LOCATION
* Name of your Data Source you can find from the 
ODBC Data Source Administrator