Basically, you’ll have to kill two other enemies with a single exploding Berserker. Sounds pretty easy but before thinking of such, it would be better for you to read these tips below:

Step by Step

1. So you need to get a Berserker to explode and kill two other enemies… when you reach the excavator and power it on.

2. Just focus your shots on the Berserker that comes up on the left. When he is weak (when he starts to glow), change to your magnet gun and shoot him with it. Now shoot close to a group of enemies and it will explode, killing some of them and unlocking the trophy.
Hint: You can always retry if you reload your last checkpoint.

Supplementary Video