@Hurremoglu when you create an approval routing you can create 2 steps with the same step no. So that User A ad User B can approve simultaneously.

The purpose of the step no is to allow users to approve document sequentially. e.g. step 10 should be approved in order to approve step 20.

In the core functionality we cannot assign a certain user to Approve the Document Revision (document state change). Anyone with Admin access to the document can change document status. So, a suggestion would be you can control who has admin rights to the document. 

@diwelk ,

When I use multiple users for the same step, both users have to approve. A single user approval should be sufficient.

@Hurremoglu then you can assign a group for the step, instead of a person. Makesure the person group includes both User A and user B. Then only one user need to approve that step.

@diwelk hi again,

user A is able to approve my step but the revision status is not advancing.

 Ah, I see now. File import user must approve status. Thanks  @diwelk .

In the Document Revision access tab, any user that has Admin rights to the document, can change the status of the document revision in the document header.

When you create a document, by default you will be granted admin rights to the document. Then you can grant admin rights to additional persons or person groups. So that they also could update the document status.