Route approval to direct manager

i’m trying to create workflow for material request doctype as below

Requester creating new material request >> only direct manager can approve his request >> procurement user start working on quotations >> purchasing manager approval >> gm approval >> finally procurement user can create the po and proceed

my issue is i have 2 users (A - B) user A is located in TEST1 department with A role profile
one direct manager A-DM for A user, whenever user B which he is located in TEST2 department with B role profile creates new material request the A-DM user can approve it! however he is NOT his direct manager

short question is: how do i limit user’s approval for direct manager only

Any help?