By convention, the rarest class is the "positive" class in binary classification.
There is an override for binary-looking values:
- 0/1 or 0.0/1.0
You can use the Script tab of an Analysis to add preparation steps before training model (e.g. find and replace) so that your target column matches one of those, then re-create a prediction task (or in your existing task's settings, click Learning taks > Redetect settings).