replace certain blocks on world gen

So... to cut long story short i want to replace some blocks of the specific block on a world gen if conditions apply....
for example if there is iron block above dirt block change that single dirt block  into obsidian...
i have procedure set however i dont know what to do to trigger it....i did try some but all of them say that trigger doesnt have required xyz dependencies....
and in other posts ive seen aditional generation options but i cant  find that...

im using mcreator 2024.4

please if you can help me id appreciate