Assuming you have a legitimate copy of Zero Hour (Origin, Steam, or Disk), here is the safe workflow used by players in 2021:
As long as you stay in "Skirmish vs AI" or "Challenge Mode," a trainer is simply a sandbox tool. Assuming you have a legitimate copy of Zero
However, users should be aware that as of 2021, many of the old hosting sites (CheatHappens, MegaDev) had moved to subscription models, while the freeware Phoenix trainer was preserved by the community on Archive.org. MegaDev) had moved to subscription models