In the Editor sidebar, look under the collapsible panel called Node properties. When you select a chance node in the game tree, this panel will let you change the chance node’s properties.
A chance node can have one or more outcomes. A chance node must have at least one possible outcome, so it is not possible to remove the last outcome.
Each outcome has a probability associated with it. The probabilities should sum to 1. If they do not, they will be scaled so that they do sum to 1. This can be useful if you want to enter the probabilities as relative weights. For example, if you enter “2” and “3” for two outcomes’ probabilities, this will automatically scale to 0.4 (40%) and 0.6 (60%) when you save.
Remember to press the Save button any time you make changes to this panel. Otherwise, your changes will not be applied to the game tree.