Data Migration
Atlassian provides the Jira Cloud Migration Assistant (JCMA) to help Jira users assess and migrate from an on-premise Jira instance (Server or Data Center) to Jira Cloud.
TestRay app data migration feature is done together with JCMA tool provide my Atlassian.
For detailed steps, please refer to: TestRay for Jira Server/Data Center to Cloud Data Migration Guide