i downloaded it then a avira warning popped up saying Virus or unwanted program 'TR/Swisyn.ajuy [trojan]' detected in file 'C:\Downloads\pleasesendh4x0rtorapture-ch\Bioshock 2 Trainer.exe. Action performed: Deny access
In a nutshell: It's how some trainers function that cause an anti-virus program to detect threats where there are none. This is known as a false-positive. The trainers are completely safe, so just add an exception to your anti-virus or temporarily disable it while using the trainer.
If you do not know how to add an exception, perhaps this page can help you: Link