ashramachandran, the "best way" is by train. If you want to look up train times and prices, go to the Swiss Federal Railways website: www.sbb.ch
Enter from: Interlaken (Ost or West, whichever you want), to: Brig and a date and time. This will always find the quickest route and show you the stops and where you need to change. Every rail route in Switzerland has at least one train per hour, so you will have plenty of options.
I just looked it up, it will take 1 hr 11 mins. and cost CHF 45 2nd class full fare. To get to Brig for 09:44 you need to get the 08:00 from Interlaken, change at Spiez, arriving Brig 09:11.
I find it curious you booked a train from Brig to Venice, without first checking how to get to Brig. Me, I would have looked up Interlaken Ost to Venezia as one query.