Use this plugin: TrainLevel.cs
Currently, this plugin go to the trainer at level 5, 10 and 15. To change it, open file with notepad and line 14 replace "5, 10, 15" by "1, 2, 3, 4, 5, 6, 7" if you want go to trainer at the level 1, 2, 3, 4, 5, 6 and 7.