Setting circumstance indoor cycle

I’d like to have a realistic speed from my wahoo speed sensor. I don’t think it matters, but I’m riding a Sunny 1805. What wheel circumference should I set this up as? Help is much appreciated!

You can measure your wheels circumference by putting a mark on your tire and aligning this with a mark on the floor.
Roll the tire one full rotation and when the mark on the tire is closest to the floor, place another mark on the floor.
The distance between the 2marks on the floor will be the tire circumference.
Select the closest option without going over.

This said, please realize speed means nothing in Zwift, your Wahoo speed will almost never agree with your game speed.
A wheel on speed sensor is an extremely inaccurate input set up for Zwift but it lets you try it out and have fun.