You can use MindMeister's built-in multi-page printing wizard.
To do that simply click on the print icon at the bottom right of your map editor:
Select Multiple pages from the bottom sidebar
MindMeister will then automatically calculate the used pages according to the selected paper format (A4 per default) and you are able to re-arrange or modify the printing canvas for the different pages.
By clicking on Print you will be able to print the selected pages and use them together for a bigger map.