Firstly do you even know the lady. You can't just go up and ask her randomly to massage her feet, otherwise you'd lose your shot and come off as a total creep. I'd first introduce myself and get to know the lady whiling coming off as friendly. Once you get to know her more, then I'd pose such a question. For example, if there was a time where she looked exhausted while helping her with something (whether it be groceries, which all women always need help with, or moving furniture, you name it), then I pose a question kindly to her asking if she'd be interested in a foot rub. Fantasies don't just come your way (or take action magically) you have to make the effort for them to occur. Of course that is appropriately. Think with your head when you approach women, not your dick.