On my '93 190E 2.3, I took a hacksaw and cut the top off right at the bottom of the ball bearing. I protected the area around the tower so no metal shavings would get into anything. Then, I was able to insert the allen wrench and press down on the spring mechanism and turn it either way to adjust the air fuel mixture. The spring stayed securely in the tower.
Below is a photo of one that someone sent me from their 2.3. I used it as a reference.
