Page 50 of manual
DRAM Frequency [Auto]
Sets the DRAM frequency.
When left on [Auto] the memory runs at memory SPD (Serial Presence Detect) specification.
F4-2400C15D-16GTZR
https://www.gskill.com/en/product/f4-2400c15d-16gtzr
If you look at specifications .
SPD Speed 2133MHz
The memory is set to run at 2133MHz when DRAM Frequency is left on [Auto].
page 50 of manual
Advanced DRAM Configuration
Press Enter to enter the sub-menu.
Here you set DRAM Timings
Beginning with Cas Latency, set the that to first number and the next three numbers in DRAM Timing Specs.
In memory specs that is listed as 15-15-15-35-2N where 2N is the "command rate" setting.
The tested voltage and SPD voltage are both 1.2v.