cpu usage how can i check my pc cpu usage for previous time

You can't.

You'll need to take a reading whenever you know you'll need it in the future and store it in a variable.

I once did the following and worked like a charm:
Took readings of CPU usage into an array every so many seconds. Maybe just 2 variables may work for you.
Then, as well, every so many seconds I "pulled down" my readings so the newest reading would take the first place in the array.

I did that with Timer "thread" from System.Windows.Forms library (be careful, cause there is another Timer class in System.Threading -of which I'm not a fan.