@nusoel welcome to the KNIME forum.
First: you should always have an independent backup strategy including provisions for accidental deletion as well as version management and disaster recovery (in case the drive gets lost).
Having said that: if the data is absolutely critical you should stop doing anything with the machine and contact a professional data recovery service (like Ontrack) since this might be the only chance to get the file back if all other measures fail. Professional recovery services can cost several $ 100 (and will usually be sufficient) up to several $ 1.000 if we are talking military/intelligence grade data forensics (but it is doable).
Then: KNIME itself does not come with any recovery mechanism (yet), the KNIME server although does. So you will have to rely on your own backup.
Often it is just a case of a misplaced knime-workflow folder. You might check this guide to familiarise yourself with the logic behind KNIME’s data storage policy: