There are a few ways:
1 Drive, but it is expensive. It is 600miles from the tunnel, ie about an 8 hour drive
2 Fly to Geneva and hire a car. Use the French side of Geneva airport as it is cheaper!
3 Fly to Geneva then take the train from Geneva to Lausanne (north of the lake, in Switzerland), then take the short train down to the water’s edge at Ouchy, then take the boat to Evian, then a taxi up the hill.
4 Fly to Geneva then take the bus from central Geneva to Thonon or Evian.
5 Fly to Geneva and use the excellent Leman Express, which is cheap and rapid.
Timetable and full information for the Leman Express (eg works on the line) is here
Buy tickets here: https://www.sbb.ch/en/tickets-offers/buy.html
