What should someone who made one or two vows during adolescence do if they don't remember the details or occasion, and haven't fulfilled them?

If the vow was made before reaching puberty, then it is not obligatory to fulfill it, due to the hadith: "The pen has been lifted from three: from the child until he reaches puberty." Otherwise, it is obligatory to fulfill it. If you are unable to recall what you vowed, then you must offer an expiation for an oath (kaffarat yamin) for each vow you predominantly believe you made.