Can't do it bro. Payday-2 is already listed in the Permanently Retired Games - Not Eligible For Voting section on page 1 of this thread. Game devs caused that, see PWiz's post on this page:
We have to abide by that.
Feel free to request another if one comes up you'd like added or even if you'd wish to vote for one already listed. Thanks.
Unfortunately I see Caliber said that they no longer own that game. But I also see an ex-mod told somebody that this trainer still works so you might try this one:
* Updated game trainers and cheats daily
* Get notified when new cheats are added
* Request which games get new trainers
* Priority support with any problem