Printing a diagram can be done via the print icon or by using File, Print… or simply Ctrl+P.

If the diagram is to be split up into several pages, this is done by first selecting the Print Range option to print the Entire diagram.

Then in the Page Setup panel,  the option to Print as poster should be checked.

The Format and Orientation options are selected according to how the diagram is to be divided up.

The page margins should be set to zero. Note that these settings will be retained and so will have to be changed back when a normal print is to be done. (The default is 10 mm.)

In the preview pane, dashed lines will indicate the page divisions. When it looks satisfactory, the diagram can be printed via the Print button.