Hi Sulagna,
You can reach Ziro from Guwahati by a taxi directly. Guwahati is 473 km away from Ziro and it takes about 11 hrs to reach by road.
You can take a train from Guwahati to Kathal Pukhuri that takes about eight hours. After that, you can hire a taxi or a bus to reach Ziro which is 122 km away from there.
You can also take a bus from Guwahati to reach Itanagar/Naharlagun/North Lakhimpur and hire a taxi or public transport after that to reach Ziro.
Keep travelling!