Hi @Mk_snow,

Assignment rules in a way that when a record is created then based on certain field value assigned to is configured . Not in a way that assignment rule is used for record producer. 

There can be OnSubmit Client script as well for setting up Assigned To value. Many possibilities so figure it out one by one.

if my response helped then you can “accept the solution” and close the thread.

Regards,

Rohit