If you have 2 x HDMI monitor. First HDMI monitor is connected from the HDMI port on the hub, and the second HDMI monitor is connected from the first primary USB-C/Thunderbolt3 port, with the USBC to HDMI cable. (See the image below)
USB-C to HDMI cable.
If you have a DVI monitor as the second monitor, please convert the DVI to HDMI port by plugging an adapter, such as the image below--DVI to HDMI adapter,
OR get the USBC to DVI cable, such as below:
If you have a MiniDP or VGA monitor as the second monitor, please get the USBC to MiniDP or VGA cable, such as below:
The bottom line is the first monitor has to be connected from HDMI port to HDMI monitor, and the second monitor has to be connected from USBC/Thunderbolt3 port on the hub