It depends a little bit on how you have your project created. If both S7 CPU and Simotion CPU are in the same project then it's easier. Open HWConfig for D435, double-click desired profibus interface and in the Operating Mode tab select Slave. Then you create configuration of IO. Compile.Afterwards open HWConfig for S7 CPU and add C2xx/P3xx/D4xx ISlave to the profibus network. Double-click it and in Coupling tab couple itto your D435. If you have two different project then you have to fill up configuration tab manually. Remember that outs on D435 must be ins on S7-CPU and vice-versa.