how do I create new screen for a bug or story

[Amrita]

My Epic link is locked , but I want to create new screen for a bug/story

[Nic Brough -Adaptavist-]

I don't know what the Epic link has to do with this question, but for the rest of it:

Go to Admin -> Issues -> Screens and create a new screen.

You'll then want to go into the project where you want to use it, and look through the "issue type screeen scheme", identifying which issue types are currently using which "screen schemes", then swapping your new screen into them as appropriate for create/edit/view.

Have a look through https://support.atlassian.com/jira-cloud-administration/docs/configure-issue-screens/ and check the links on the right for more on the three areas.