how can I unpickle cherries they are tooo tart /
These are pickled cherries? You can always balance tartness out with something sweet - sugar, honey, etc.
Try to convert to a rumtoft ... drain and rinse the cherries, put in a (clean) glass jar with a one part sugar / three parts rum. Let sit for a month then taste ... might be a nice sweet and sour taste with a hit of booze.Use medium dark rum, not white rum.
Another sweet and sour switch would be some kind of preserved chutney. Sounds good! (So does rumtoft.)