Where do you pour the transmission fluid in a 2005 trailblazer

Make sure all shifting linkage is properly hooked up. how are you checking the fluid. it should be done while hot running and in neutral . Make sue all lines are connected. a dirty trannie filter will do this also. You could have possible got a bad transmission iy happens all the time.

Low transmission fluid

Yes!!!
If you have no junk yard where you can buy a dipstick, see if there is a transmission repair shop where they will sell you or even give you a dipstick from a "core". Short of that, you could speak to someone in a parking lot or a Chevrolet dealership about borrowing their dipstick out of their 2005 Trailblazer just long enough to check your fluid, and then give it back to them. If you get a dipstick that is the wrong length, sometimes you can re-mark it to fit your transmission with a nail-file or something.
Be blessed.

The fluid should be changed at the 100K mark. The front and rear differential fluids should also be changed at that mileage. The transfer case fluid needs to be changed every 50K miles and only use GM Autotrak II gear oil.

pour the fluid in the tube where the transmission dipstick is located, add only a pint at a time and recheck

Get a small funnel and pour the automatic transmission fluid into the transmission through the dip stick tube (fluid level check tube).

Most of the car dealers recommend to perform Maintenance services scheduled at 30K, 50K, 90K and so on.
At 30K they mostly inspect all the systems, and replace fuel filter.
At 60K they inspect systems and flush must of the fluids, transmission oil and filter, coolant, brake fluid, differential and transfer case fluid, and replace the air filter. Some replace the spark plus at 60K some at 100K.
At 90K all timing belts are replaced, and the status of the timing chain checked. A deviation of more than 5 degree means, there it is the time ayes on the timing chain.
At the Owners manual for 2005 Chevrolet Trailblazer recommend:
Inspect all the systems at 25K, and replace fuel filter.
Replace engine air cleaner filter, automatic transmission fluid, automatic transfer case fluid every 50K.
Replace spark plugs every 100K.
Maintenance Services for your car are scheduled at 25K, 50K, 75K,100K and so on. All are tune ups but they are not the same.
The only concern for GM is the GM Dex-Cool antifreeze. There are some complaints regarding this product. I recommend to flush the cooling system every 50K to 60K.

Hi!!
The transmission fluid is poured thru the transmission dipstick tube, you'll need a small funnel to do this. Do not overfill.
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oh the side of your transmission, above the halfway point, there will be a plug that you can open. (don't open the plug on the bottom of the transmission as that's the drain plug). When you open the plug, some fluid should leak out meaning it's at the right level. If nothing leaks out, pour some fluid in until it starts to run out and then replace the plug.

automatic transmission fluid is filled directly through the same tube the transmission dipstick goes...a long neck funnel and slow pouring followed by constant level checking is best never overfill the transmission