Official (revised) guidance from Hyundai.
When the GPF warning light illuminate, please perform the following driving pattern to activate the GPF driving regeneration. (Speed >80km/h (50 mph), 3rd or higher gear with engine rpm between 2500-4000 rpm)
Drive over 80km/h (50mph) in 3rd gear Accelerate up to 4000 rpm, release acceleration pedal, wait 5 sec and accelerate again to 4000 rpm.
Continuously repeat this process until the GPF warning lamp will switch off.
In case of DCT (dual-clutch transmission) is necessary you switch to SPORT mode and change gear manually to 3rd or higher gear then follow mentioned procedure.
In case you drive over 30min / or the GPF Warning starts blinking (at this time LCD warning message will be displayed, we recommend you, to let the GPF system be checked by an authorized workshop