How do I restart the Switch?

Holding the power button (located on the top of the Switch) opens a menu that gives you the option to power the system off entirely.

To answer the problem, rather than the question though: I had a similar issue with my wi-fi not long ago. Rather than powering the system off and on again, I found it was enough to cycle the network adapter by putting the system in Airplane mode and then taking it out, which is in the same home button menu as the sleep option.

Use the power button on the top. The Home button is only used to put the Switch into sleep mode.