How to replace certain blocks

I was bored on Minecraft, and so I created a Superflat world with villages. Is there any way that I can replace all of the Gravel to say... TNT? I felt like being destructive, and I was wondering if there would be a faster way than manually replacing each of the gravel with TNT by hand. I don't use WorldEdit because it sadly will not run on my computer.
Best Answer
This is simple to do with the /fill
command. (1.8+ only)
Syntax:
/fill [x1] [y1] [z1] [x2] [y2] [z2] [BlockToFill] 0 replace [BlockToBeReplaced]
So in your case it would be:
/fill [x1] [y1] [z1] [x2] [y2] [z2] minecraft:tnt 0 replace minecraft:gravel
This will replace any gravel between the two co-ords with TNT.
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How do you fill to replace certain blocks?
Type the command in the chat window and press the Enter key to run the command. This /fill command would replace all blocks in the fill region, including air. The replaced blocks will be dropped and can then be collected as if they were mined with a pickaxe or shovel.How do you replace a specific block with WorldEdit?
How to use WorldEdit to swap and replace blocks in MinecraftHow To Mass Replace Blocks! | Minecraft (Xbox/PS4/PE/Bedrock)
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