Push to Talk Buttons

When the engineer set up the buttons on all of our phones, he put a "overhead paging" button removing one of the employees.  I need to remove the overhead paging button and place the removed employee back on the screen.  I have looked everywhere I know and cannot find any info on how to do this.  We have had our phones since the very end of February and I have had little help in getting all of this down.  

Thanks in advance.