how to change wp upload directory to another domain directory

Question

Well, what you want to achieve saving uploads in another domain? You want to share the uploads folder with another domain?

Did you know you can use more than one domain (site) in a single WordPress Installation? It’s called Multisite:
https://premium.wpmudev.org/blog/ultimate-guide-multisite/

To change the upload dir. Just use the filter upload_dir. It’s documented here:

Be happy!