Same process that has been used before to make simpler parts. Take a donor organ (lungs in this case) and dissolve out the cells, leaving the collagen “framework.” Collagen is basically the glue between the cells, so what you have left is a ghostly 3D model of a complete set of lungs. Then, seed the lungs with cells from the intended recipient, soak the scaffold in a nutrient bath for a month, viola! A new set of questionable lungs, ready for human trials in about 12 years. To be tried out on pigs first, apparently.
The new lungs are said to be less dense than natural lungs. I’d imagine they’re pretty squishy and probably fairly easily damaged… cough good and hard and you might tear ’em in half. One would hope that in time they’d become good, proper lungs, but testing over a span of years should answer that.
I would imagine that within a decade-ish, 3D printers may well be able to print out collagen scaffolds for any of a number of organs, the basic CAD model being adjustable for various needs and sizes. And it may be possible to 3D print the scaffolds with the cells already in place… lab-grown cloned good cells from the recipient, each cell individually placed. The end result *might* be a lung, say, printed out in a few hours, ready for implantation in… I dunno, a few days? For those with genetic flaws, then the cells might be cloned genetically engineered cells, with the flaws removed, perhaps derived from reverse-engineered stem cells taken from the patient.