so how do i convert these links so it links to a federated (backup) content on other Lemmy instance/s?

Paste the link in the search bar of another instance. If the post is cached, it'll return it. Ideally, use the link to the post on the original instance, rather than the link to the post on another instance.

Technical answer:

Instances store posts from other instances. Every post on the fediverse has a unique ID called the "actor ID". The actor ID of a post is the URL of the post on the instance of the user that authored the post. On the Lemmy web UI, you can retrieve this by right-clicking on the rainbow star icon below any post and copying the link.

To retrieve the details for a cached post, you can call resolve_object?q=<actor-id>. For example:

https://sh.itjust.works/api/v3/resolve_object?=https%3A%2F%2Flemmings.world%2Fpost%2F41938713

For convenience, the Lemmy UI calls this when you paste a URL in the search bar.

This can work for any URL that points to the post, but you should use the actor ID where possible. The Lemmy backend knows the actor ID of every post it has, but it may not know whichever URL you're querying with, and you may get a null result when the post is cached.

I hope this helps.