Direct To button!
By the sounds of it i am guessing you are a student.
I seem to remember being taught
1) Pull out your WAC i am here and i want to go here, guess the distance/heading turn onto it
2) work out a rough estimate
3) advise flightwatch of flightplan amendment
4) pull out ruler measure the track and distance and work out an accurate ETA
Remember its not rocket science. Remember to keep flying the aeroplane
Aviate Navigate Communicate.