Hi @Ganeshm1 ,
You can write a assignment rule [sysrule_assignment] to map the assignment group, there you can write the script that will run only when the assignment group on incident is empty.
Or, while creating an incident via alert management rule, you can map the assignment group in create record action in create incident subflow, for reference you can refer OOB create incident alert management rule there you can refer the OOB subflow as well in the alert action tab
