Have a read of this:
https://www.volvoforums.org.uk/showthread.php?t=275839
Another method is to remove the upper trans cooler hose from the radiator and connect some hose to the radiator, put the other end in a jug. Start the engine and run until 1 or 2 litres has drained.
Pour the same amount of fresh in through the filler tube. Depending on the start condition, do 5-6 litres. Go for a drive, check levels, do more if necessary.
There's some intructions here:
https://www.ipdusa.com/products/4809...sion-flush-kit