Unfortunately this is one of those levels in which you rely solely on luck. You have to be lucky with special candies because that’s the only realistic way to clear the Jellies on the Conveyor Belt.
Every time you clear a candy on the Conveyor Belt you should pause for a second and check whether you can match candies on the Conveyor Belt. The opportunity to do this won’t occur often and you don’t want to miss out on that opportunity.
Keep in mind that candies move from the upper half to the bottom half of the playing field so match candies near the bottom half as often as you can. Doing this will shift the largest amount of candies, hopefully start a chain reaction and create new opportunities to make special candies.
While matching candies at the bottom it can be easy to ignore making special candies at the top of the playing field. So pause after every move and glance at the entire playing field to see whether you can make special candies.