I don’t think you can migrate, since if that was possible your “karma” would also be able to move with you. People have been asking for that recently, but others have been saying that the Lemmy software doesn’t support that.
I think the best thing you can do is make a new account on a new instance and look back at the rest of the fediverse from that instance.
I believe Mastodon is a different software compared to Lemmy. Lemmy is an aggregation software of the entire Fediverse, while Mastodon is more like Twitter. My limited knowledge of Mastodon makes me think that it wouldn’t be possible to see Lemmy instances, but if you sent your comment using Mastodon then there might be a chance. Hopefully someone else in the comments will sound off.