How to print A2 spread as 4 A4 in InDesign?

In such cases you can use the tiling options in the Printer Settings, to let a larger page size be split up into smaller printed sections.

But there's a snag: almost every office and household printer is not capable of printing across the full page. So you need to keep a fair amount of printer margin in mind for the design of the spread, in order to split one A2 into exactly four A4s with a decent overlap. Otherwise you'll an extra array of A4 pages to print the remaining edges of the A2, as you can see... Another easy way to make it all fit, is to just scale the printed size down a bit, within the range of the printable area plus overlap.

Which version of InDesign and OS?

Is this document to be printed on your desk-top printer or put out to a commercial printer?

The layout is not clear from your decsription – is this a 4 page A4 leaflet (i.e. A3 printed both sides and folded on the long edge)?