If I understood you correctly there were some issues with the license and for easier handling you decided to wipe the existing installation - because the data is not needed anymore and you want to start fresh.
If so, you would just need to delete jira (installation directory) along with jira_home (home directory). Additionally you would need to delete the database.
Then a new installation with the license key you said it would be valid until 2021 is needed.
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