Well you're half way there then if you've written before. Some people will tell you that scriptwriting is a talent only a few posess, but from my own experience I can tell you that it really isn't the 'Holy Grail' it seems.
If you've written before, you really just need the tools and a few pointers to start writing scripts. There are specifics but essentially, story telling is not that much different.
The place I mentioned does do a correspondence course (one of the writers is actually a BAFTA winner and has even written a feature film, but doesn't shout it about too much because you get goodness knows who sending scripts through.
While a few are okay, when you start receiving ten a day it can be a problem.
Anyway, I wish you all the best with your search.
If you require any further guidance please don't hesitate in contacting me. I'm happy to point you in the right direction.
Not sure if I can put my email up, but will anyway and if I'm not supposed to, a moderator can always take it off.
Best regards
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