WorkFlow

Step 1: Open Project Settings → Open Issue Types

Step 2: Click on the edit WorkFlow

Step 3: Create new fields and create a flow as shown below.

For automation
Step 4: Click on any Transition and then click on +sign on the right side of Rules.

Step 5: Click on Assign issue to someone and assign them issues automatically. (After every QA is passed i.e. after Post Dev QA, Post Stage Qa that task should be assigned to PM, Scrum master so they can assign it, relevant person.