After the first sparge, tap off three litres to allow space for the second lot of grain. Keep that aside until the 2nd sparge. Program the second mash and add a mash out if you like. Mash out then sparge with another 10 litres.
Reiterated mashing is a process in which you create a wort from your first runnings and then use that wort as your strike water for essentially your second mashing.