Avoid downloading pre‑built trainers flagged for “build 091.” If you need a gameplay advantage, learn to use yourself on an offline copy, or install a rebalance mod. Better yet – embrace the challenge: JA:BIA’s difficulty is part of its enduring appeal.
As for the trainer, I couldn't find any information about an official trainer for build 091. However, there are various trainers available online that can provide advantages such as unlimited health, ammo, or money. jagged+alliance+back+in+action+build+091+trainer+top
If you want to adjust difficulty or “cheat” safely: jagged+alliance+back+in+action+build+091+trainer+top