What should a person do who forgot whether they uttered an oath or a promise to God, when the promise was in the heart?

A mere intention to take an oath or make a vow does not make anything binding, nor does it necessitate expiation. Rather, it is essential to utter the words with the tongue. If a person doubts whether they uttered the words with their tongue or not, the default is that they are free from obligation, and no expiation is required, especially if they are prone to obsessive doubts (waswasa); in such a case, they should cast aside these doubts.