Most of the logic for the bot finding who to shoot is done within C++. This Service(BotSearchEnemyLOS) calls functions within the ShooterAIController, which is a C++ class, so you would either need to change the logic within ShooterAIController or make your own logic within Blueprints.
I would recommend using AI Perception and EQS for creating your custom bot logic. If you don’t know how to use these, Epic has a great tutorialon how to use them.
This is the Service that finds the bot’s enemy.
You could change it to this so it only picks the player as its enemy. This is far from the optimal way to do this though.
Alternatively you could delete BotSearchEnemyLOS from the BotBehavior tree. Then create a new AI controller that extends from ShooterAIController. Then set the bot’s enemy to the player (like I did in the BotSearchEnemyLOS Service) with the Begin Play event. Once again this isn’t the best way to do this, but it is a quick way to get what you want. Like I said before, I recommend using the AI Perception and EQS to get the Bot to do what you want.