The default Courant number of 5 is quite conservative for this type of problem on a mesh of reasonable quality, so it can be increased to speed convergence. Once the solution has reached the stopping criterion of 300 iterations, open the Solvers node and select the Coupled Implicit node.
Set the Courant Number property to 10.0.
Open the Stopping Criteria node and select the Maximum Steps node. Set the Maximum Steps property to 1500. This will instruct STAR-CCM+ to iterate 1200 steps in addition to the 300 already done.
The maximum steps number of 1500 is a reasonable setting, in this case, to get to convergence. Normally, you would not know ahead of time what a suitable iteration count is. You could either set a large iteration and watch the residuals or a monitor plot, or you could add a stopping criterion based on a monitor, assuming you know a value that the monitor would have once the solution was converged.
Click on the 
(Run) button to continue running the simulation.