Jblk_U1, Jblk_D1: Base Clock Plus, Minus Connectors; Power1, Reset1: Power Button, Reset Button - MSI MEG X399 CREATION Quick Start Manual

JBLK_U1, JBLK_D1: Base clock Plus, Minus connectors

You can use these connectors to connect the external buttons. Press the button
connecting to JBLK_U1 to increase the CPU base clock or press the button connecting
to JBLK_D1 to decrease the CPU base clock.

POWER1, RESET1: Power Button, Reset Button

The Power / Reset button allows you to power on / reset the computer.
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Overview of Components
JBLK_D1 (short the jumper to decrease
the CPU base clock)
JBLK_U1 (short the jumper to increase
the CPU base clock)
Reset button
Power button