There is no built-in solution for this. For Excel there is a trick that does a best-effort migration, you do loose some things.
- Create a Tree based query in Azure DevOps that has all the work items you want to migrate
- Open Excel
- Use the Team tab to pull in the work items you want to migrate
- Click New List and connect to the source organization
- Select the Work Item Query you created in the first step
- Click Choose Columns and add all columns
You now have the data you want to import in one excel file. Create a new excel file to push the data to the other account:
- Open Excel
- Use the Team tab to pull the work items
- Click New List and connect to the target organisation
- Select the Input List so you're not bound to a query
- Click Choose Columns and select all the same columns in the same order
- Click Add tree level and convert to parent child
- Repeat Add tree level to match the depth of the source excel
- Copy all the fields from source to target excel file
- CLEAR THE ID COLUMN ON THE TARGET EXCEL FILE
- Fix issues that appear (usernames, area paths, project name etc)
- Hit Publish to create the work items in the target organisation.
What gets lost
You will loose the following:
- HTML formatting
- Attachments
- Links other than Parent-Child
- Some dates will reset (Created, ...)
- Some process workflows may prevent creating work items in the correct state
- Custom board columns
- Revisions of the work item
Alternative
There are tools like Martin Hinshelwoods Migration Tools that can replay work item history from one account to another. It takes a bit of effort to update all the configurations, but it will do a much better job at copying your work items over.
See: