There is a limit for exporting. You can start to get some information here;
You did not indicate server vs. cloud, but the easiest approach is to break it into smaller groups - maybe use a created date to build chunks. You can then combine them afterwards.
The link is for Jira, but service desk is probably the same.
For JSM June Challenge #2, share how your non-technical teams like HR, legal, marketing, finance, and beyond started using Jira Service Management! Tell us: Did they ask to start using it or...
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