To upload your data via CSV, you need to have image URLs that are publicly accessible. To create these URLs, you can use a feature offered by AWS, as it allows you to create image URLs for every S3 Objects (a.k.a your image files). Once you have the URLs, follow these steps to upload these URLs on Suite:
Follow the guide below to make your S3 Bucket public.(https://docs.aws.amazon.com/AmazonS3/latest/user-guide/block-public-access-bucket.html)
Follow the guide below to make your S3 Object public.(https://docs.aws.amazon.com/AmazonS3/latest/user-guide/set-object-permissions.html)
Follow the guide below to make your S3 Bucket CORS enabled.(https://docs.aws.amazon.com/AmazonS3/latest/user-guide/add-cors-configuration.html)
Once you are done with these settings, your URLs for S3 Objects will be publicly accessible and CORS enabled, which also means that you can upload your images via Suite.