You might have to contact the manufacturer if can't deduce the thread type of the connector.
That said in a pinch you might be able to take the next smallest from your kit and apply enough Teflon tape to the threads to make it work. Just be gentle with it. A lever bleeding/fluid top off is a gravity feed and not under pressure
That’s really bizarre. I got the same kit recently and it comes with a whole bunch of fittings, both for the syringe and the funnel.
It took me a little while to find the correct fitting. Are you sure that any rubber washer in the lever housing came out as well with the cover screw? There might be something in there causing the kit’s fitting(s) not to thread.