To overclock Avalon 721 you should use Cgminer –
Here is the official git repository – click here
–avalon-options <arg> Set�avalon�options baud:miners:asic:timeout:freq:tech�
For overclocking your device we will increase the frequency and configure the hardware components to increase the clock speed of the machine. Remember that overclocking will void your 60 days warranty provided by Canaan. Be careful while increasing frequency you may lose your�device.
For best hash rate and life of your miner use this command
–avalon-auto Adjust Avalon miner’s frequency dynamically for best available hash rate
You will receive the best hash rate for your device after measuring internal and external temperature and humidity of the place where it is kept.