BPT Example created with the 3 roles as given below,
1. Creator : Create the Task
For this you can application registered users like "BPTExampleUser".
2. Assigner : Assign the Task to Reviewer
Create Role with the Name "Assigner". and assign this role to one user.
3. Reviewer : Reviewer review the Task
Create Role with the Name "Reviewer" and assign this to different user.
Modified the screen flow and clean the data