I have about 250 blog entries, each with a standard EE file field that points to a file on the same local server EE is running on. I've installed the Assets add-on and set up an external source (an Amazon S3 bucket). I converted that standard file field to an Assets field pointing at that S3 bucket and it's working beautifully!
When creating a new blog post the file uploads to S3 without a hitch. Now onto the old posts:
What I need to do is to tell the Assets field to look for the image on S3 and not in the local filepath. I can manually move those images into place on S3, but I don't know what to do on the EE side to update the DB so Assets knows where to look.