This is the most common way to unblock a user if you are on a computer.
If you have previously blocked a user in Google Chat and wish to resume communication, you can unblock them directly within the Chat app or via your Google Account settings. how to unblock someone on google chat
If you cannot find the user in your block list, they may have changed their account status or username. You can try searching for their email address in the search bar; if they do not appear as blocked, you are likely already connected or the block has been lifted. This is the most common way to unblock