So I have an extra Cooler Master 120 Air Flow fan that I wanna add it to my Cooler Master MasterAir MA410P but is it ok to add an air flow fan to a cpu cooler and if it is ok how should I attach it? Air blows in or out?
It might help, it might not. Additional air flow would help, but the actual effect will not be to reduce your CPU temperature, because the automatic fan speed control system will still be aiming for the same temp. Thus what it might do is to slow down your existing fan slightly when it is being helped by the added one. If you do this, mount the extra fan so it pulls air out of the radiator, moving it in the SAME direction as the existing fan. To fasten it on, I doubt you can duplicate what the original design has - a bracket that holds the fan to the fins. You might need to resort to using nylon cable ties to hold the added fan in place on the rad fins.
Then you have the issue of how to power and control the fan. Since both fans are 4-pin type and on the same CPU cooling system, I suggest you get a simple 4-pin fan Splitter like this and use it to connect both fans to the CPU_FAN header
NOTE that of the two output male connectors, one is missing its Pin #3. Use that output for the old fan you are adding. This ensures that the CPU_FAN header will still receive the speed signal from the existing fan on the cooler, but the added fan's speed will NOT be "seen" anywhere.
This actually might cause a problem in one circumstance. This is an older used fan. IF it fails and stops, it becomes a hindrance to air flow, rather than an assist, and that would reduce the performance of the cooler system. Since that added fans speed swill not be monitored for failure by the mobo header, YOU will need to check it from time to time to ensure it still is operating properly.