Uneditable a request assigned to a technician

Uneditable a request assigned to a technician

Hi,
A request assigned to a technician in a group can be edited by other technicians in the group. How can I prevent this from happening? I want when a request is assigned to a technician, that technician can make fields of that request uneditable for other technicians, and other technicians can only view the request or define a work log.
Thanks.

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