Since you have posted this in Publisher section, so it seems and I assumed that you are running a QV Publisher. If yes! Then open your QlikView Management Console. Under Status tab go to Tasks tab and edit the task for which you want to increase the Number of tries.
Just done some quick research in this regard. Actually Number of tries for execution of task is based on Timeout i.e. 24 hrs (1440 mins) here. So you have to enter an average task execution/completion/failure time in Timeout so that it will give it another try.