I have over 500 songs where I have to search manually 
Well you can use the Find Lost Tracks utility to change the path because it looks like some of those have a wrong path with twice the /Users/nelecolic/ in there.
If the resulting new location already exists it will not be able to change the paths, but you can use the Force option there to do it anyway.
Subject: Issues with Missing and Duplicate Songs in Lexicon
Hello Christiaan;,
I’m disappointed that Lexicon isn’t working as expected. It’s a great idea, but there are some issues. Although I managed to reconnect all the missing songs, after reopening Lexicon, many of them are still marked as missing. In my library, these songs even appear twice or three times.
I hope you can help me fix this problem.
Thank you and best regards,
Nele
Can you show me a screenshot of the locations of those same tracks?
Tracks don’t just appear 3 times in Lexicon, they must have been added or imported there
Only song that I’m missing is in the playlist, the others are without playlist
I have synced my iTunes library. I didn’t have a duplicate.
Okay first delete the tracks without playlist from Lexicon, see this guide: How do I remove tracks that are not in any playlist?
Then let me know again how the library looks and what duplicates you still have. The Find Duplicates utility will probably be able to fix it for you. You can try it after doing the above guide, just make sure to make a quick Lexicon backup first because then it’s easy to go back if needed.
I’ve now done what you wrote, but I still have a lot of missing songs that the Lexicon can’t find and they’re all on my computer!
Okay try selecting all the missing tracks (CMD+A) → right click → Relocate. Point it to the
folder that has those files