In Change reqeust, when a record is in Assess State , I can only change that state to Authorise, I am not able to move back to New state , how can I move back to new state and display state is New.

[Madhurya]

In Change request, when a record is in Assess State , I can only change that state to Authorise, I am not able to move back to New state , how can I move back to new state and display state is New.

I want to keep New also one of the options in the below screenshot. ( state fields) Currently when the record is in Assess state, it displays only Assess and Authorize. 

Where I need to change the code to make sure "New" state also appears here?

[Aman Kumar S]

All these state values transition are handled by state transition handler, even if you manage to show New state on the form, it will be lot of work to adjust in the script includes and workflows, and will cause maintainability issue going forward during upgrades. Approvals are also generated, which you will need to cancel before going to New.

As per the OOB, once change goes to assess, and approvals are rejected then the state goes to New state, if you still want to go ahead to change this, also keep in mind the points that I have mentioned above

[MattSN]

This is covered in the change docs. You'll need to update the script include for the change type and likely a UI Policy as well.

Configure state model transitions

As pointed out by @Aman Kumar , the problem you'll run into is that Assess genreates approvals, so at this point you're better off cancelling and copying the change so that the approvals are reset.