Specifications and the board diagram don't show that though. I think that part of the manual is copy pasted from another manual or a misprint. Either that, or the rest of the manual is wrong. Based on these, taken directly from the manual for that board on the ASUS website, there are ZERO three pin RGB headers on that board.
2 x Aura RGB Strip Header(s)
1 x Addressable Gen 2 header(s)
2 x USB 2.0 connector(s) support(s) additional 4 USB 2.0 port(s)
1 x M.2 Socket 3 with M Key, type 2242/2260/2280/22110 storage devices support (SATA mode & X4 PCIE mode)
1 x M.2 Socket 3 with M Key, type 2242/2260/2280/22110 storage devices support (SATA mode & X4 PCIE mode)
1 x SPI TPM header
8 x SATA 6Gb/s connector(s)
1 x CPU Fan connector(s)
1 x CPU OPT Fan connector(s)
3 x Chassis Fan connector(s)
1 x AIO_PUMP connector
1 x 24-pin EATX Power connector(s)
1 x 8-pin ATX 12V Power connector(s)
1 x 4-pin ATX 12V Power connector(s)
1 x Front panel audio connector(s) (AAFP)
1 x System panel(s)
1 x Clear CMOS jumper(s)
1 x COM port header
1 x USB 3.2 Gen 1 (up to 5Gbps) connector support additional 2 USB ports
ASUS TUF GAMING X570-PLUS (WI-FI)1-3Chapter 1
Layout contents
Connectors/Jumpers/Buttons and switches/Slots Page
1. ATX power connectors (24-pin EATXPWR; 8-pin EATX12V_1; 4-pin EATX
12V_2) 1-15
2. CPU, CPU optional, and chassis fan connectors; AIO pump connector (4-pin
CPU_FAN, 4-pin CPU_OPT, 4-pin CHA_FAN1-3; 4-pin AIO_PUMP) 1-14
- SPI_TPM connector (14-1 pin SPI_TPM) 1-10
- AM4 CPU socket 1-4
- AURA RGB headers (4-pin RGB_HEADER1/2) 1-17
- DDR4 DIMM slots 1-4
- Q LEDs 1-8
8. Addressable Gen 2 header (4-pin ADD_GEN2) 1-18
- USB 3.2 Gen 1 connector (20-1 pin U32G1_12) 1-12
- M.2 Socket 3 1-16
- AMD Serial ATA 6 Gb/s connectors (7-pin SATA6G_1-8) 1-11
- Clear RTC RAM jumper (2-pin CLRTC) 1-9
- System panel connectors (20-5 pin PANEL) 1-13
- USB 2.0 connectors (10-1 pin USB78, USB910) 1-12
- Serial port connector (10-1 pin COM) 1-15
- Front panel audio connector (10-1 pin AAFP) 1-10