This post function assigns an issue to a user within the specified role automatically, if your selected field matches the value entered. For instance, you can define a post function to assign issues automatically to the escalated user's project role within the transition Start Progress, if the priority of the issue is critical.
To add the Assign to Specific User Role Based on Issue Field Post Function
Go to the transition of your workflow, switch to the Post Functions tab and then click on the Add post function link.
Select JEP - Assign to Specific User Role Based on Issue Field Post Function and then click the Add button.
Just select the project role that the issue will be assigned to, select a field and enter the matching string. If the value of the field matches with the value you defined then the issue will be assigned to a user in that project role.
Click on the Add button and that's it.
Please bear in mind that if you use this post function within Create Issue Transition, the post function should be placed right after the Creates the issue originally statement.
Do not forget to publish the workflow!