Do you mean how do you reset the Default Field Configuration's settings?
There is a "Restore Defaults" option in the field configuration which should restore operation values - hide/show, required/optional, renderers, etc. To access this as a Jira Admin:
^ This should do the trick. If not, let us know and we can advise further :)
So you are trying to get back the default field configuration which was present earlier.
So before following up on @Stephen Wright _Elabor8_ answer please ensure that whether the existing configuration is required or not? If required do the necessary, if not the existing projects might break down. Ensure to take a copy of the existing configuration.
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