This will convet a Lottie json file that doesn't have "ty" properties at the beginning of the object to one that does.

convert.js

const fs = require('fs');

convert = (json) => {
    if (typeof json != "object") {
        return json
    }
    for (var key in json) {
        if (json.hasOwnProperty(key)) {
            json[key] = convert(json[key])
        }
    }
    if (!!json["ty"]) {
        const ty = json["ty"]
        delete json["ty"]
        return { "ty": ty, ...json }
    } else {
        return json
    }
}

const file = JSON.parse(fs.readFileSync(process.argv[2]))
const converted = convert(file)
fs.writeFileSync(process.argv[2].replace(".json", "_conv.json"), JSON.stringify(converted))