You can do these in two way…easy way or the hard way!
Start your flight plan beyond the airport, so you will have to fly manual from take off until you can pick up your first way point.
When you copy your flight plan from Simbrief or FLTPTOIF, paste it into notes on your iPad or tablet. Then open up the airport charts, select the aappropriate SID and then note down the extra waypoints. Add these on to your flight plan in your notes section (after your departure airport code and before your first waypoint). Then copy the whole of the new flight plan into Infinite Flight. You might need to “tidy up” some of the way points after it has loaded up so it flows correctly, then you are ready to push back!
Good luck and happy landings.