If no sound is heard from the internal speakers of the KIYOLA KF-20 or KF-25 after unplugging headphones or earphones, a conversion plug (adapter) may still be left in the Phones jack. Confirm that nothing is connected to either of the two Phones jacks, then turn the volume knob to adjust the volume.
If a headphone plug or adapter plug is broken and cannot be removed from the Phones jack, the piano needs to be repaired. Contact an authorized Roland retailer or Roland support (Backstage, Roland Account required).