I doubt your chainring(s) (the gears at the front) are worn to the point they need replacing, probably the smaller cogs out back are OK, too. Get a new chain and have it installed--if shop is not familiar with Bromptons, have them measure off the old chain instead of traditional chain length methods. This may not need to be done, but I have no idea if the fold means you need more chain than usual?
Ride it with the new chain: if you get skipping out back or chain suck up front, then you'll need to deal with those components, but I bet you don't.
Lube your chain. Once a month, or after any wet ride. You'll need to replace a chain as early as 3k mi if you don't care for it, 5-7k mi if you do. You can usually get 2 chains of use before you need to replace the cogs out back.