How can I replace my front cog... or fix slipping off on folding bike? I have a Faulkner folding bike and I notice often the 6th gear, high gear falls off switching to high gear. Someone mentioned that the cog might be a bad choice for the front of folding bike and may be why it has the plastic guard around it - not just for keeping it off your pant leg.

It's generally been falling off and pulling the guard off, which it sticks in now... the deraileur high setting seems right as I moved it a bit and had other problems... it stays in the right gears adjusting it back.

Should I take the cheap plastic guard halves and the little screws screwing them together and replace with screw+bolts to make it more secure, maybe insert a metal shim? or replace the whole front crank? I found this but it doesn't list a place to size and purchase replacement front cog. https://www.downtube.com/pages/convert-to-triple-chain-ring-should-you-do-it/

EDIT - Here's a picture of the problem crank:
If a new chairing is the solution, then the best chainring to solve your issue is a 1× specific narrow-wide chainring. I'm not able to identify your crankset/chainring interface from the Amazon link. Once you know this, you can see if there's such a chainring available or if you'd need to replace your crankset entirely (probably too expensive to be worth doing on this bike).

I would also be tempted to check if you can shorten your chain by one link. This would mean that your rear derailleur would hold the chain on the chainring more tightly.