Cloud - Migration Tool
If you already have a version of Issue Picker Custom Field Type for Server/DataCenter, you can import all your issue pickers with their values, config and contexts to cloud using the Issue Picker Migration tool. First you will need to create de Json import file , in your Jira Server / Data Center go to Manage Apps -> Issue Picker Migration Tool , select projects to import and then export fields.
Json import file created
Now in Jira Cloud , Go to Apps → Issue Picker Migration Tool