In image view | editing mode, click button RGB Adjustment on Editing Panel, a dialog allows you to choose the adjust the RGB values of the image.
Move the slider of R(red), G(Green) and B(blue), the effect will be reflected on the image. Click OK when you are satisfied with parameters you adjusted.
To save your editing, please click button Save in the toolbar on the top.
To undo or redo your editing, please click the tab Editing History on the bottom of Editing Panel, all your editing history is listed and click one of them to roll back.