Problem Definition

At the moment, for user attributes, the data must use account id value.

Suggested Solution

It will be best if the admin can use their email address instead for an easier process to import user attributes.

Workaround

Admin can get user Account Id from "Export User" file at User Management and update the CSV file accordingly: How to import Jira User Attributes to Assets via CSV with either Atlassian Account or Customer IDs
You can also use Automation to update the user type attribute of the corresponding user as detailed in this article: Update user type attribute of an Insight objects using Automation after Import