When students say "i can't do it" what is a good response to give them

Ask them, "Why can't you do it? "Show me how you are trying to do it."

When my students say they can't do it, I usually ask them to do as much as they can and I will help them when they are stuck. Sometimes, just standing beside them as they work is enough to build their confidence.

Say "yes you can, just keep trying" but if they still can't then help them understand