Is preparing oneself for fasting, such as using a miswak to ensure no food remains in the the mouth, considered a [valid] intention for fasting Ramadan if one forgets to make the intention after the 'Ishā' prayer?

Forming the intention for an obligatory fast must be done at night, meaning from sunset. Whoever conceives the thought that he will fast tomorrow, at any part of the night, has formed the intention. If he resolves to fast, then the legally required intention has been achieved. The intention does not have a specific manner or a specific wording. However, if the thought of fasting tomorrow does not occur to him at any part of the night, then he must make up that day.