A study that is already in progress can't be generated. The outcomes are being generated.
Click Cancel in the Job Status dialog box. Canceling is possible before one iteration of any outcome is generated. If the generation is canceled successfully, the tokens are not consumed.
If an outcome iteration is generated, you can't cancel the generation and tokens will be consumed.
Wait for the current generation to be finished. Then, you can modify the setup of the generative study and generate outcomes again.