i have the json ready but how do i replace it

yeah me 2 i have no idea
"DTD",
"TET",
"DTD"
],
"D": {
"item": "Minecraft:diamond_block
},
"E": {
"item": "Minecraft:elytra"
},
"T": {
"item": "minecraft:totem_of_undying"
}
}
}

i tried this but no work