Uploading file to DigitalOcean Spaces using s3 bucket from backend (nodeJs), get Access to only frontend (react)

I am trying to upload the file on Digital Ocean server from the backend (nodeJs) using s3. File uploaded successfully but I want that file only access by my frontend (React).

The code of uploading a file from nodeJs like this -

        const AWS = require('aws-sdk')

        // Configure client for use with Spaces
        const spacesEndpoint = new AWS.Endpoint('nyc3.digitaloceanspaces.com');
        const s3 = new AWS.S3({
        endpoint: spacesEndpoint,
        accessKeyId: 'ACCESS_KEY',
        secretAccessKey: 'SECRET_KEY'
        });

        // Add a file to a Space
        var params = {
        Body: "The contents of the file",
        Bucket: "my-new-space-with-a-unique-name",
        Key: "file.ext",
        ACL: 'public-read'
        };

        s3.upload(params, function (error, data) {
          if (error) {
            return reject(error);
          }
          return resolve(data.Location);
        });

I have no idea how to set the correct permissions on the s3 bucket. I am new to the digital ocean so give steps from the beginning.