When importing Executions Results, it is possible to set the Reporter or Assignee using a multipart endpoint.
In the multipart endpoint, it sends a second file in JSON format with the additional fields and respective values to set up.
And the format to use for the Reporter or Assignee is the following:
{ "fields": { "reporter":{"name":"charlie"} } }
For additional information on all the available multipart endpoints, please check Import Execution Results in our documentation.