I bet the board uses 4 jumpers or 4 dip switches to set the vcore.
If no jumpers (all off) are 1.8V and 1.9V is a single jumper (or dip switch on) to either the right or left side of the jumper block then moving that jumper one step twords the middle of the jumper block will give you 2.0V while adding a jumper instead of moving the first one will give you 2.1V.
The basic idea is that the jumpers are worth 0.1, 0.2, 0.4 and 0,8 volts over the lowest Vcore value with the 0.1V jumper at one side and the 0.8V jumper on the other, the manual should let you figure out which is which.
Do NOT test this if all known vcore values dosnt match what I have written.
New PC: i9 12900K @5GHz all cores @1.2v. MSI PRO Z690-A. 32GB DDR4 3600 CL14. 3070Ti.
Old PC: Dual Xeon X5690@4.6GHz, EVGA SR-2, 48GB DDR3R@2000MHz, Intel X25-M. GTX 980ti.
Older PC: K6-3+ 400@600MHz, PC-Chips M577, 256MB SDRAM, AWE64, Voodoo Banshee.