As får as i know, joins are not available in the data manager. To execute a join you will need the script editor.
For the most situation you can work around the need of using Joins in qlik sense by adding the join data as a separate table in the data model. You might get a more snowflakey datamodel, but for the most it will work.
Plees ekskuse my Swenglish and or Norweglish spelling misstakes