Not able to change the task from story to subtask

[Theres Parthiban]

I was trying to move task from story to sub-task, as soon i changed to subtask it took me to new window and it was asking to choose the story from the dropdown but i'm unable to choose and click next 

[Vickey Palzor Lepcha]

Please provide some more information.

When you say that you are unable to select the Parent Issue ( STORY ) what do you mean ?

Are you not able to find the STORY under which you want to add this new STORY turned SubTask in ?

I hope you know it already that you need to select a new STORY or Task now and add that new SubTask under it .