How would you approach solving a math problem to someone when you dont understand the process?
The way to approach is is to work with the student in their knowledge and to makle sure they understand the steps and you can ask the the student of how they got it and then to review of their work to make sure it makes sense. When I had tutored someone in pre calculus online there were formulas that were on that I havent been familoiar in a while so as when the student was working I had skimmed through fornmulas of trig functions and explained those in the applications of what the student was working and if I didn't know any topic I would say to come back to that question later.