How to say "Please find your own change" in English?

I just watched a movie "The Wretched". When the boy was going to checkout at the grocery store, he happened to meet the boss and ran to fish (this plot setting is a bit brainy?) The boss left a piece of cardboard at the checkout counter "Make your own change."   But what's worse is that the boy stretched out his hand to take out the money in the change slip, but was seen by the boss' guard dog and thought he was going to steal it. The boy whose money was barked by the dog had to touch his nose and put the bill back. Then again, we can say "find your own change" in Chinese. Change is "find". Of course, I have also seen Americans say "Find your own change." " "Basically if you'd like to get a coconut water or coffee, its on the honor system so find your own change in the can." Usually this idiom unless you're in a foreign country or you'll occasionally see it in the media Other than that, I can't learn it under normal circumstances, so I immediately pressed the pause button and used the Baidian Kuaisou App to memorize this phrase.