DIAGNOSIS The Switch outputs video via its dock's HDMI port, not directly from the USB-C port on the console itself (without special adapters). You likely connected the monitor's HDMI to… nothing, if you tried from the Switch tablet.
FIX You must use the official Nintendo Switch dock. Connect the dock's HDMI out to the InnoView's mini-HDMI input. The monitor also needs separate power via its USB-C port—use the provided cable and a USB power adapter (like a phone charger). The Switch dock provides power to the console.
IF THAT DIDN'T WORK Ensure the monitor's input source is set to HDMI. Use the side buttons to bring up the OSD menu and select "HDMI" as the source. Also, try a different HDMI cable between the dock and the monitor's adapter.
HEADS UP You cannot power the monitor directly from the Switch dock's USB ports for video; they don't provide enough power. You need a separate power source for the monitor, making this a two-cable setup (HDMI + USB-C power).