Need to know what year it is, it makes a difference.
I haven't done this on my Blazer yet but my manual says to reach up behind the bumper to the light socket, twist it and it will come out of the housing with the bulb so you can change it.
More information is required to properly answer your question. Are you referring to the turn signal bulb, flasher or switch? SWITCH
2057 bulb you can find it cheap at walmart.
how to change front left turn signal bulb on a 2004 chevy express
Answer : unscrew the signal lens and remove the signal bulb and replace with 1157 bulb reverse process
194 For side marker/front, 1157 for front and rear signal/park lights
The answer is detailed very well at our enthusiasts forum at www.trailvoy.com
How to change the bulbs in the climate control for a 1999 Chevy trailblazer
According to my Haynes manual you reach up behind the bumper to the back of the light and turn the socket and pull it out so you can change the bulb. I believe it turns counterclockwise 1/4 turn to release it.
1995 Chevy Blazer turn signal light bulb replacement: Purchase the correct replacement turn signal light bulb(s) first, before disassembling the vehicle. See sources and related links below for replacement bulb information. Then consult your owner's manual for the turn signal light bulb replacement procedure. As simple as it sounds, the owner's manual is the best place to start for bulb replacement instructions and illustrations. You may want to consider replacing both left and right at the same time in order to keep brightness and color equal (optional).
For the front turn signal on a Chevy S-10 you remove the parking lamp lenses and replace the bulbs. If it is a rear turn signal bulb the taillight lenses will have to be removed to access the bulb.
Change the turn signal switch in the steering column, or the turn signal relay.