Yes, you can say that.

Technically, it's not wrong, but it is more correct to say "You can't (can not) do it."

*Is this the correct way to say this* is how you would ask this and to answer this if you are unable to do something you would say *I'am unable to do that* or *I cant do this*

hi you can say ( you can't do that ) or ( you can't do it ) or you not able to do it and you unable to do it , this , and that ........... all correct and you perfect