how to Download file in react native from base64 string? Can someone help me with this?

const { config, fs } = RNFetchBlob;
let PictureDir = fs.dirs.PictureDir; // this is the pictures directory. You can check the available directories in the wiki.
let options = {
fileCache: true,
addAndroidDownloads: {
useDownloadManager: true, // setting it to true will use the device's native download manager and will be shown in the notification bar.
notification: true,
path: PictureDir + '/Testing.pdf', // this is the path where your downloaded file will live in
description: 'Downloading image.'
}
};
config(options).fetch('GET', 'africau.edu/images/default/sample.... => {
console.warn(res);
alert('HIIII');
});

I tried this and its working with URL; But how to deal with base64 string?