hi ricson
welcome to the forum
it's a simple enough drive, follow the signs for Rethymnon, which takes you on to the national road, drive west for around 50 minutes to the (signposted) Spili junction, which is basically at rethymnon, turn left there following the spilli road, about 20 minutes later you take a turn right for plakias as signposted
easy peasy!
opps beaten by Mr R