How to burn

import { Address, toNano, WalletContractV5R1, TonClient } from "@ton/ton";

import { mnemonicToPrivateKey } from "@ton/crypto";

import {
    AssetsSDK,
    createApi,
} from "@ton-community/assets-sdk";

async function main() {
    const client = new TonClient({
        endpoint: "https://toncenter.com/api/v2/jsonRPC",
    });

    const MNEMONIC = process.env.MNEMONIC;
    if (!MNEMONIC) throw new Error("Set MNEMONIC (space-separated words)");
    const keyPair = await mnemonicToPrivateKey(MNEMONIC.split(" "));

    const wallet = WalletContractV5R1.create({
        workchain: 0,
        publicKey: keyPair.publicKey,
    });

    const provider = client.provider(wallet.address);
    const sender = wallet.sender(provider, keyPair.secretKey);

    const NETWORK = "testnet";
    const api = await createApi(NETWORK);

    const sdk = AssetsSDK.create({
        api,
        sender,
    });

    const JETTON_WALLET_ADDR = Address.parse("JETTON_WALLET_ADDR"); // placeholder
    const jetton = sdk.openJettonWallet(JETTON_WALLET_ADDR);

    const RECEIVER_ADDRESS = Address.parse("RECEIVER_ADDRESS"); // placeholder
    await jetton.sendBurn(sender, 1200000n);
}

void main();