Sorry, I made a leaflet in PS. The mode is RGB. Can I print it? Should printing be changed to CMYK mode?

You'd better change it to, you must have seen the color jar of the printer, right? Generally, it is four-color printing, and all four tubes are connected. They are four-color interfaces: C, M, Y and K. CMY is the initials of three printing inks: cyan, magenta and yellow. K takes the last letter of black, and the reason why it doesn't take the first letter is to avoid confusion with blue. So it will be better to change to cmyk color.