Solution: 

Step 1: Place the cursor before the merged reference and click ‘Enter’. 

Step 2: Select the reference and go to ‘Edit’ menu. 

Step 3: Click ‘Move to previous’ option. 

By doing this, the reference part will move to the previous section.  

Step 4: Click ‘Move to next’ to move the reference into the back matter. 

Step 5: Click ‘Structure Reference’ option from Edit menu to update the ID sequentially.