If you encounter someone tailgating you avoid speeding up but if possible try to get into another lane if there's another lane and it's possible to do so.
This will let the tailgater get out from behind you and let them on their way.
Although it can be tempting to do so. Never slow down enough to where the tailgater could hit you from behind.
When I encounter a tailgater I try to move into the next lane or pull off to the side of the road to let the tailgater get by which reduces stress on me when driving once the tailgater is no longer behind me.