Please follow below steps
1- Update Robot type as ‘Unattended’ and provide the password for the robot user in password textbox/field
2- Go to Platform.uipath.com → Services and verify Unattended robot allocation - pls refer below link for https://docs.uipath.com/cloudplatform/docs/distributing-your-licenses
3- Go back to Start Job window and verify - robot will be available for allocation.