How to restrict the agent to do not use these below field or how to make this happen ?

[Neeraj Kumar]

How to restrict the agent to do not use these below field or how to make this happen so that only admin created fields will be shown in form only

[Florian]

I cannot tell for sure if this works in Jira Cloud as we use the Server edition. But here is my idea. 

You can remove the fields you don’t need from the screen (settings->issues->screen) or place them on a second tab (settings->issues->screens). 
When you put all the fields you don’t want to be touched on a separate tab you can then us the plugin JSIncluder to hide the tab completely with some JavaScript. This is not easy but it can be accomplished with reasonable efforts as Jira comes with JQuery by default. 

Below an example. First we see two tabs. Then we see the JSIncluder script. Last wee see a screen and the tab is gone for good.

[Trevan Householder]

@Neeraj Kumar Just remove the fields from the screen - native functionality in both cloud and server.  I recommend against using tabs - problematic and not intuitive (although I have come across one or two use cases where I actually agreed a tab was a decent approach - it's very rare).

[Angélica Luz]

Hello @Neeraj Kumar,

Thank you for reaching out to Atlassian Community!

On Jira Cloud, there are no options to disable or hide the Configure fields button. Agents will be able to select the fields when creating the tickets the same as administrators.

There is a feature request suggesting the implementation of such ability:

• Disable / enable "Configure fields" button

Please, click on vote and watch to receive updates about the feature.

Regards,
Angélica