Found this answer in a similar question. It wasn't the Accepted answer but it doesn't require any Add-on and I believe it's applicable here:
This method can be used without any add-ons or plugins tested on JIRA OnDemand (Cloud). Also note you can probably use excel format for import but I prefer CSV. I tested this first by creating 3 issues before updating live data, I would suggest you do the same to become comfortable with the process. JIRA Administrator rights are needed for this method.
Go to Search for Issues in JIRA.
Identify all the issues you wish to update.
Adjust the columns to show your summary, issue key, and field with values(Due) to use.
Click export and select a format, for this example Excel (current fields).
Clean up the file, removing unnecessary columns, and everything but the header and data rows (export adds extra rows of footer/header content).
Go to JIRA Administration drop-down and select "System".
On the left pane under the heading "Import and Export" select "External System Import".
Choose file and select your CSV.
Select your project. Note you may need to adjust date format at this step.
Map your fields. You must have issue key and summary!
- Issue Key (CSV field) => issue key (JIRA field).
- Summary (CSV field) => Summary (JIRA field).
- Field to use values (CSV field) => Field to update values (JIRA field). In my case it is "Due Date" => "Original Due Date".
Click next and it will perform the update and indicate the result.
Hope this is helpful and if it is, please click the Accept check-mark - thanks!
Thanks Nic and you're right that one cannot change the field, only move the data to a new one (then remove the old one if appropriate).
Laura - Do these posting answer your question? If so, please click the "Accept as Solution" button so others know it does. Thanks!
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