How do I start the cleaning cycle when the CLEAN/DESCALE light is flashing?

Insert the 1 CUP filter basket into the portafilter, followed by the supplied cleaning disc and 1 cleaning tablet, then lock the portafilter into the group head and place a large container beneath the spouts. Press the POWER button to switch the machine off, then simultaneously press the 1 CUP and 2 CUP buttons, and also press the POWER button, holding all 3 buttons for approximately 10 seconds. The cleaning cycle will last approximately 5 minutes and two beeps will sound when complete. (Page 23)

From the official Breville Breville Bes870xl A Barista Express Machine User manual, page 23

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