You must first install and enable the module using the module admin in unembed issabel pbx.
Not sure if it will work, but you can try:
create a new boss/secretary group
in boss extension set the extension you want to restrict, in your case '1000'
in secretary section, use also '1000' (this part is the one I am not sure how it will work).
in chief section, set all the extensions you want to be able to call 1000, in your example, 1001,1002, 1003
chief extensions are the only ones allowed to call "boss", but the module makes any calls to "boss" ring "secretary" instead, so, maybe setting both to the same extension will achieve the result your are looking for.