I need step my step how to change a timing chain on 2007 mazda cx7

First, DO NOT start the engine if the mechanical timing is wrong! My next obvious suggestion is to get it to a good mechanic and get them to sort it out for you.
I'm assuming your refering to the Mechanical Timing? Mazda use an 'Interference' engine so read this all the way through BEFORE doing any work. An interference engine means the valves will hit the piston face if the mechanical timing is even slightly out. That is why you don't start your engine with the timing set wrong. It's a VERY expensive repair.
Start from scratch. Remove the chain from the CAMs and cable tie it to something on the top of the engine to stop it disappearing out of sight.
Turn the Crank to about 10 to 15 degrees past Top Dead Centre (TDC). This is to move the pistons away from the valves so you can set the Cam timing marks. Set the Cam marks first then turn the Crank BACK to TDC. As long as the chain marker on the crank sprocket is lined up correctly the Cam chain markers should be correct.
Once you have timed everything into place use a socket and ratchet to turn the Crank pulley bolt Clockwise 2 full rotations. The timing marks should return to the correct positions.

The torque the engine produces, or a bolt torque?

year make model engine torque
year make model (the part) torque specs

https://www.google.com/search?q=2007+mazda+cx7+engine+torque+specs

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could be time for a new timing set. depends how many miles are on the engine and if something has gone wrong. they don't last forever and the belts need to be change every 75k to 100k to save doing damage to the valves and piston if it were to break. the chains will last a lot longer but still wear out

Oh no,
Are you replacing VVT and chain? You need 2 special tools for this.. 1 to hold the camshaft where the slot is for the high pressure fuel pump, and another beside the crank damper on the rear of the motor, there is a small 10mm bolt that you remove and install a "holder" of sorts that holds the crank at TDC.
If you fail to do both of these steps before removing the chain you run the risk of throwing the timing out. Part numbers are as follows for the SST's.
Camshaft: (picture 1) SST 303-1061 (49 UN30 310610)
Crankshaft: (picture 2) SST 303-507

There are 3 Nuts inside the Engine Compartment, There is one Bolt on the Lower Arm and you have to remove the ABS and Torsion Rod. You need a Spring Compressor to do this job.

There are no timing marks, special tools are needed. The Mazda dealer should have been the only one to work on it. Mechanics never want to work on "Basket Cases" because of the time involved in the job. It turns a good job into a money loser. See if the dealer will at least set the timing marks for you, and you can do the rest without any liability to them. No one wants to do a job like that and then the customer wants a guarantee that there are no problems. The timing chain alone is a 5-6 hour job.

vvt actuator and you are driven by timing chain not belt common problem in cx-7

The Powertrain Warranty should be good for 60k or 5yrs. This is a common problem. Fix it and get rid of it before you have to shell out $6k on a new engine.

it should have be changed at about 750000 mi ,belt...and for the most part look things over your self even before u go check fluids, serp..belt, check for cracks ..proper air in tires ...and so on

you need to take it to your local dealer and raise a big fuss because this is a known problem and if you yell loud enough you should be able to get this fixed under warranty.