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Personal issue search fields customisation is available under configuration icon on the issue search bar. (YOUR_JIRA_URL/secure/ExtensiIssueSearchUserConfiguration.jspa)
Global search fields customisation is available for JIRA administrator in Administration → Add-ons → Issue Search (YOUR_JIRA_URL/secure/ExtensiIssueSearchGlobalConfiguration.jspa)
Configuration screen allows to customise main search fields located in the first row on the search bar and optional extended search fields located in the second row.
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