Follow below steps:
1. Connect to both data sources separately.
2. Then select a dimension/measure from one source and then go to the 2nd source and click on like button next to fields to link them and use data blending.
3. Create a calculated field to join them by using IF and the linked field like this,
IF ATTR([TABLE1].[link field])=ATTR([Table2].[link field]) THEN 2nd field
4. Now you can have a field from both the sources into the created field.
Hope this helps you.