You can help to steady your partner's mind and ground their thinking in practicality. If they have the tendency to dream and fantasize rather than make solid, workable plans, you'll have an especially beneficial influence in their life. In another lifetime you were their teacher, and you gave them just the sort of mental shaping and guidance that you can give them again in this life.
They will look up to you on an intellectual level, because they'll know you have a sharp mind and an eye for practicality. They'll take your advice seriously and will be open to learning from you. You can help them to learn to express themselves more clearly and effectively. If they are shy or insecure about their intelligence or how they present themselves to the world, they will very much appreciate your input, even if yours turns out to be a short-term affair. They will model their self-expression after your advice in some way, which will help to further them both intellectually and also at a karmic, evolutionary level.