The Iterations panel in Analysis Setup allows you to change the numerical relaxation parameter for both flow rate and pressure. It is recommended that you use only 0.5 or 1.0 for pressure relaxation, but lower values of flow rate relaxation can be very helpful.

A good first step is to lower the flow rate relaxation to 0.05 or 0.1. By lowering the flow rate relaxation you improve AFT Fathom's ability to obtain convergence. The cost is slower run times. In some cases accepting the slower run times that come with flow rate relaxation is the only means of obtaining convergence. You can lower the relaxation values as low as you want, but it is recommended it not be lowered below 0.01.