Consolidating multiple Jira instances
The process of consolidating multiple Jira instances is exactly the same as the migration process described in Migrating Jira projects.
For the complete documentation on Migrating Jira projects, see here.
While the end result is different, the approach, tools, planning, and overall staging procedure are the same. To consolidate multiple Jira servers into one, you need to use the Configuration Manager for Jira to merge system and project-level configuration data, user-generated data, third-party party add-on configuration, and other related information. To ensure consistency in your merger, a comprehensive analysis, testing, and staging of the consolidation efforts should be performed prior to rolling out the changes of your final merger. Any errors, gaps, conflicts, and merge-specific issues that you identify should be resolved during the analysis phase of the consolidation process.