How to add estimation to the subtask?

[qsdbih]

We have set the board to use Original time estimate e.g. in work hours, days and weeks. 

So how do I add estimation to the subtasks? I cannot do it during the subtask creation or when I edit existing subtask or even if I go the subtask details. 

I don't see any option to add Estimation like I can do it with the regular task. 

[Nic Brough -Adaptavist-]

Make sure the "timetracking" field is

a) Not hidden in the field configuration for the sub-task types

b) On the sub-task issue types' "create" and possibly "edit" screen

But.  Don't.  JIRA Software (JIRA Agile) does NOT take account of the estimates on sub-tasks in the way a lot of people expect it to work (because there's different ways of doing it and Atlassian have opted to code for none of them)