The 6pin PCIe power connector is provided by the power supply, not the motherboard, double check your power supply connectors.
Even if your power supply has none you could use of x2 of it's molex connector via a dual molex to 6pin PCIe adapter (sometimes provided with the graphic card)
6-Pin PCI Express Power Adapter Cable - Dual Molex (4-Pin) to PCIe (6-Pin) >> https://www.ebay.com/itm/6-Pin-PCI- Express-Power-Adapter-Cable-Dual-Molex-4-Pin-to-PCIe-6-Pin/181774923445?hash=item2a52a136b5:g : OI8AAOSwKrhVcWIz