If you encrypted it on the way in. You can’t. The only thing you could do is grab ALL THE (encrypted) THINGS, decrypt all of them (I guess in the user’s browser? possibly on the backend via an SSA? you don’t say if you have the encryption key, but if you do that sort of defeats the point, does it not?..) but at any rate you’ll have to grab ALL the items in question, decrypt them, and then search through that.
What are you encrypting, anyway? Your database is already encrypted at rest (and “you” don’t actually know how to decrypt it), so there’s little you can do to enhance security over the normal Bubble features like privacy rules.
(Anything you do there is simply duplicative: “I took the data and encrypted it and, unbeknownst to me, it was encrypted again! And then, when I asked for it, it was unencrypted, but still encrypted with the encryption that I had put on it and now I can’t search it!” ← this is what your post reads like)
Of course, you could do something boneheaded and expose something that’s supposed to be private to users other than the users who are supposed to have access (by, for example, not having correct privacy rules in place), but that’s on you.
You might want to go read this, which (if you read it) will probably illuminate you a bit: Josh: Request for a Security Q&A Guide - #18 by josh (when you get to the section titled " Is there a way to add additional levels of protection to specific data in Bubble?", read it carefully and perhaps read it again).