Unfortunately, there is no way to recover a deleted issue unless you had a backup to restore it from, or having a plugin for that, such as: Who deleted my issues for Jira Server.
This question has been asked before, perhaps you can find additional information on this community post: https://community.atlassian.com/t5/Jira-questions/Is-it-possible-to-recover-a-deleted-issue/qaq-p/847299
Hopefully this answers your question.
Good thing you have a backup.
The restore process will depend on the type of backup you have.
The import will also depend on the Jira version you are running, kindly make sure that the guide you are using matches your Jira version.
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