This is a very common "false positive." Antivirus programs often flag trainers because they modify another program's memory, a behavior common to malware. If you downloaded from a reputable source, it is generally safe. You can add the trainer file to your antivirus's "exceptions" or "whitelist" to prevent it from being deleted.
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If you are playing on Steam, might be overwriting your edited local file with an unedited cloud backup. Disable Steam Cloud Sync in the game's properties menu before copying your edited file into the folder. Achievements Are Not Unlocking This is a very common "false positive