You can edit the image sources when uploading the image or through the Media library.
When uploading or editing the image using the Image block in the block editor you should find the image source fields in the block settings on the right.
You can edit the image source in the media library.
- Go to Media > Library.
- Click on the image thumbnail
- Find the fields on the right
Through Missing Sources page
Go to Media > Missing Sources.
Here you find images that don’t have a source yet. Simply click on the image title to go to the image edit page where the image source settings are located.