From that [post #24], steps 1–4 is to determine if your main SD card is fake, faulty, or dying. The full Write + Verify has to be done on the card starting empty or else the result can't be trusted. If the report states "The media is likely to be defective.", that card must be retired. There's no point moving forward with a bad card as that'll just be a waste of effort and will further corrupt your savedata and files.
After the SD card's hardware condition has been sorted out where the card is determined to be still good or that it has been replaced with a good SD card that passes H2testw, steps 5B–10B fixes the Nintendo 3DS folder by dumping intact titles back into CIAs, backing up their saves, supplying replacement CIAs for titles found to be corrupt, creating a fresh set of title.db & import.db by reinstalling those CIAs, and finally restoring the saves to complete the repair. After all said and done, you should finally be able to then install Ever Oasis (EUR) on your rebuilt main setup.
Edit - Before you begin steps 5B–10B, it would be a good idea to keep a copy of the Nintendo 3DS folder on your computer for safety. This is if you encounter an unexpected interruption while dumping those titles back into CIAs and extracting+decrypting their saves.