Plutonium

Open the console command in game and execute:
statsetbyname plevel <levelvalue> (to change the prestige the range is 0-11)
statsetbyname rankxp <xpamount> (to change your xp amount see this page for the required xp for each level: https://callofduty.fandom.com/wiki/Call_of_Duty:_Black_Ops_II/Ranks)
If you don't know how to open the console here is the guide: https://plutonium.pw/docs/opening-console/