how to set back my genuine windows 10 here in my dell inspiron 3252 desktop?

hi there! can anyone here knows how to get  my genuine windows10 back to my PC?

i just bhought  this dell inspiron 3252 with pre installed win10 64bit, but i need is windows 7 32bit only, which is already phasedout on microsoft market, so i bhought also windows10 32bit knowing that is a downgradable to win 7 32 bit, unfortunately the product given to me is FPP which is not downgradable and all is turn to failure, what can i do now to set back my bundled OS?