If you didn't place bookmarks, screenshot it or otherwise take notes back when you handed in the data, then the only way to find "your" first discoveries is to use the Visited Stars filter and click on each star, one by one, to see if your name appears there. There is no in-game method of listing or easily finding all your personal First Discoveries. And unfortunately, First Discovery tags are not fully journalled, so the third-party tools cannot extract that information directly either.
Using an external tool (eg. EDD/EDSM) can give you a list of what it believes are your first discoveries. For example, in EDSM you can go to My Flight Log and click on "Show as List" - any system in the list with the little yellow star is one where EDSM recognizes you as the first visitor. However, this list is "first reported to EDSM", which is not the same as "First Discovered" tags in-game, for several reasons.
- Not everyone uses EDSM, so only a subset of discoveries are in the database. Many veteran explorers do use EDSM, so it's a reasonably large subset, but it's still just a subset. And a lot of discoveries were made back before game journals and EDSM were invented. You can easily be "first to report a system to EDSM" and still not be the one with the Tags.
- EDSM's reporting happens instantaneously upon discovery (unless you've switched that off and are updating EDSM manually), whereas in-game Tags are only applied when you sell data. So, an EDSM user can discover and report a system, but they haven't yet returned to port to sell the data (and claim the Tags). Or maybe they exploded and lost the data, or maybe they stopped playing and have no intention of ever coming back and selling the data. In which case, those systems will be "discovered" in EDSM but not actually Tagged in-game yet. The reason some people switch off automatic uploading to EDSM is they are worried someone will trawl through EDSM, find their discoveries, dash out and steal their Tags.