Hehe, I wasn´t aware there was such a Step-by-Step tutorial.
The BiomePlacement probably Changed with a MineCraft update.
There are some ways to find the Biome you are looking for: You can always check the Biome you are currently standing in with: /tc biome (Because F3 will only show Plains if you are inside a custom biome)
Look on the BiomeMap.
Further down that tutorial it explains the BiomeColor setting. Basicaly, you give the Biome a Color. (Please note that the Color should be unique, and you will need to look which color other Biomes have)
If you are standing at the Coordinates 0,0 ad you use /tc map it will generate a Picture in your ServerFolder.
The Center of the Image is 0,0 and each Pixel are 4 Blocks. so if your Biome shows up 100 pixel to the left of the Image center its at -400,0
Use Generation Mode: "FromImage" rather than using the RandomMode for your world Generation you can use (inside the WorldConfig)
With that you need to provide further down a BiomeMap (like the one that gets Generated with /tc map) and TerrainControl will generate the world exactly like that. Its still 1 Pixel = 4 Blocks. Then you know exactly where your biome is located.
Apart from that:
If you are standing in your Custom Biome and you want to Tweak it:
For regenerating the whole world, you dont need to delete the whole world Folder, just the Region folder inside is enough. That way your current Player Location is saved and you dont need to move again to the Biome.
If you have WorldEdit installed, you can lookup minor Adjustments on the Fly. You dont need to reboot/delete the world for small adjustments.
Just edit the ConfigFiles, save them. Make. /tc reload
then you can use //regen from WorldEdit to regenerate a part of the world, the settings should take effect there.
That way you can easily see what has changed.
Note: This is not very reliable on complicated Generation, it can happen that TC just crashes on that Approach. But for small testing stuff it should work quite well.