HI,

If you are creating the Routing and BOM from the automated action, you can easily assign the routing to BOM if you use Python Expression. While creating the routing you can assign it to a variable and that variable will have the value like mrp.routing(5) , so using .id you can get the id of the newly created routing.

Then while creating Bill of Materials you can pass this ID.

See the Below Sample,

routing = env['mrp.routing'].create({"name": record.name})
bom = env['mrp.bom'].create(
    {"product_tmpl_id": record.product_tmpl_id.id, "routing_id": routing.id, "type": 'normal'})

Thanks