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Kindly help us to modify the Issue type
Do you mean you want to re-configure what an issue type is? Or you want to change the issue type of an issue?
reconfigure issue type
For the general configuration of an issue type, go to Admin -> Issues -> Issue type.
Once an issue type is associated with a project (via the "issue type scheme"), it becomes a structural thing you can configure for the project, so that may be where you need to look to "reconfigure".
That is done at two levels
So the next question is what you want from "reconfigure" as there's a lot that might change, and we don't know what you're trying to achieve.
I want create issue type Test to upload test cases
Test cases do not really map very well to Jira issues, they're very different things.
I would recommend looking to one of the test management apps in the marketplace and letting that handle the issue types it might need.
However, if you are going to stick to plain Jira, then it's Admin -> Issues -> Issue types -> Add