DME, or Distance Measuring Equipment, is a measuring tool for accuracy for approaches/procedures. When DME is used, it will usually accompany a station to base that distance off of (most commonly at VORDME at or very near the airport).
Currently, there is no default method to measure DME in Infinite Flight, although there are add-on apps to let you be able to use this resource. If you can find the facility where the DME equipment is located, and it exists as a waypoint in IF, you can add it to the end of a flight plan and use said waypoint as a quasi DME marker.
In your aforementioned procedure, you would tune into the listed DME facility, then make your turn to 070 upon reaching 3.5 DME from said facility.