How to set approval based on Job level for procuremnt contract

Summary:

We are required to set rules based on Job level. Whichever person will be submitter workflow should flow based on person's parent position hierarchy?

Eg:- If there are two BU and two different department

Departments A & B

person X in departtment A and BU 1

person Y in departtment B and BU 2

So, desired requirement is if X is submitting document then workflow should flow based on his parent position hierarchy & if Y is submitting document then workflow should flow based on his parent position hierarchy.

if possible then please share any document that would guide complete walkthrough make this scenario.