Not everything is in the owner’s manual. I’ve got a 2009 facelift Octavia current mileage ~1500. I have fortuitously found that twisting the trip reset stalk anti- clockwise, with the ignition off, gives the current service prediction of 15500 miles. Easy.

Must be different on the FL dash, but the trip reset button shouldnt twist!

Turn ignition off on stage, press and hold trip reset, days and mileage to service is shown.

Mine has a heavily knurled spindle so it was an obvious thing to twist it. Pressing re-sets the odometer and the total mileage can be viewed as well.