How to move a particular design in fsm Mobile

Dear All,

I need to move a particular design I'd from one environment to another, please suggest in this.

Below is the issue explanation

Let's say we have 2 development environment and one testing environment.

Dev1 

Design_name          Design_id

Field Service             1

DesignTech                2

Dev2

Design_name               Design_id

Field Service                  1

DesignAud                     2

2 groups of development teams working in 2environment  and we need to merge this in testing environment.

Our expectations here is if merge it should be like below but it not happening

Test

Design_name          Design_id

Field Service             1

DesignTech                2

DesignAud                  3

Observations 

When we import design file from import/export functionality from design screen from Dev1 and put it in Test then Test will be like Dev1. And again we import file from Dev2 and deploy in Test then it override the Dev1 design and here we can see Dev1.

Can anyone suggest me how to merge 2 designs from different environments to one environment. 

Can we take only DesignAud to another environment 

Please suggest