If you subscribe to a moderation list on Bluesky and the list includes a user that you don't want to be blocked, e.g. if you think they were blocked by mistake, there is currently no way to unblock them specifically while staying subscribed to the list. That is, there is currently no way to make an exception for a user you think has been unfairly placed in a block list, or that you simply want to follow despite the fact they do belong in the block list. There is no way to override the blocklist with your own personal allow list. This concept simply doesn't exist in Bluesky yet.
The only way to unblock them is to unsubscribe to the block list.
Open Issue
There is an open issue with a proposal to add this feature.
FR: Personal "exceptions" from subscribed mute/block lists
[...] opened on Jul 10, 2024
Sometimes when you're subscribed to a long-running mute list there are situations where you'd want to make an exception for a few accounts.
https://github.com/bluesky-social/atproto/issues/2634 (accessed 2025-01-18)
Note: in the issue there is a mention of a clever way to solve this by creating derivative lists with boolean logic. I don't think anybody needs this. We just want to make exceptions in exceptional cases.