There should be a blue button marked "OC Genie" on the motherboard, with a power button next to it.
Turn off the PC.
Remove side panel.
Press blue OC Genie button.
Replace side panel.
Turn on PC.
If there's no such button on the motherboard, enable OC Genie in BIOS Setup.
Then "Save & Exit".
https://forums.geforce.com/default/topic/486372/overclocking/how-do-i-use-msi-oc-genie-/