A problem about how to change the training points style in the overtraing plot?

Hi all,
I have a data style problem in the plot below.Now I would like to change the points style(red and blue points)of the training sample ,but actually I could not even choose these points because there is another layer over these points(you know what I mean?)I have to delete the layer above to make a change of the points style.I would like to know is there any other method that I could change the points’ style without delete any elements of the plot .Thanks so much!!!

May be @moneta can help.