Jira admin configuration
Create a custom field in Unified Diagram Viewer type to store digram syntax. please refer this KB for more details and steps
You can create more than one diagram fields per issue/project
Select Settings then Work items(new view)/Issues.
Under FIELDS, select Custom fields.
Select Create custom field. Make sure to select All/ Advanced to view the Unified diagram field type.
Select Unified Diagrams, then click Next.