You do
not need any "PCIE 1x cable" to plug your GPU (MSI GTX 1060 Armor 6G OC) into the motherboard (MSI B350 PC Mate).
The GPU itself has a PCIe x16 bus/interface and is just plugged
directly into your motherboard's
PCIe x16 slot (the second slot from the top, after the small PCIe x1 slot, labelled #9 in the photo below):
The GPU then has an
8-pin socket on its side and will require an
8-pin (or
6+2pin) PCIE power cable
from your PSU to power it.
The 8-pin socket on the GPU looks like this:
Your 8-pin (or 6+2pin) PCIE power cable looks like this (depending on your PSU model):