Work Order Creation Not Possible while assigned order type as header level work center

Hello Experts,

     While creating a work order through Work Manager when assignment type is set as Header level Work Center, the fields Main Work Center, Work Center Plant , Priority , Planning Plant are disabled.

Please suggest how to resolve this issue so that I will be able to create a work order through it. Any suggestions on this topic wil be appreciated.

Thanks & Regards,

Raj Kumar