Steps for picking up the French Horn

Dear Sir or Madam,

When I was 7, I attended the school's band and played a simplified version of the French horn (also the violin and the flute). However, my interest lies in the piano and I gave up French horn after a year. Pay attention that we can only afford something like a French horn (EDIT a natural horn), not a real one.

Now I am a part-time concert pianist, I was thinking why not pick up the French horn again. And then there is the first complete French horn in my possession. Unfortunately, I have kind of forgotten everything and while I am waiting for a teacher (who won't be available in a month), is there something I should do to pick it up. I am sorry but I have basically forgotten everything.

Thank you soooo much.