Freshrelease has an option for you to easily move all your data from JIRA. If you are the account admin,
1. Click on your profile picture > choose Account Settings
2. Go to "Import from JIRA" > Authenticate your JIRA account
3. Choose the projects you want to import from JIRA
4. Choose the custom fields you want to import from JIRA
5. Click Import
Important info:
1. Use "https://" in your account url. Eg: https://acmeinc.atlassian.net/
2. Use an API key that belongs to an account admin. API key can be found at https://id.atlassian.com/manage/api-tokens
Once all your data has been imported, you will get an email confirmation.