Hi there @Wilko1806,
sure there are ways to learn KNIME better! Check this topic for more info: How to learn more ?
Also this one can help: Update Database output
Now to your use case. For better understanding I have created an example workflow which is attached. Check it out and if any questions feel free to ask. If you don’t know regex wanna check with some expert does it covers all cases 
2020_05_18_Delete_Duplicates_3_or_more.knwf (17.1 KB)
Br,
Ivan