How do I find a previously discovered system?

One possibility is to use the scan for discoveries from the galactic map.

In the 1.03 version of the game on consoles this is d-pad up and on Windows tab is bugged, but trying x could work.

After I had jumped to several star systems away, I used this feature and found my already discovered systems.

This enabled me to locate where I had been and allowed me to warp back.

According to a post by IamI3rian yesterday on Gamefaqs:

If you enter the galaxy map you'll have the option to search for discoveries. All discoveries. This means yours show up too. Just click find closest... etc and you're all the way back to where you need to go, without much hassle. You might need to enter freemode once or twice if you're jumping far, then short then far again at certain points, but it's not tough.

Just look for the named stars.

Source: https://www.gamefaqs.com/boards/739857-no-mans-sky/74158734

Quote is from the very first post.