I foolishly managed to get my 2017 MBA locked in target mode

Just as the first gentleman, in the beginning - I found this now, of course. Lol. I was told by the Genius Bar that at some point I set a password to my FileVault feature. Encrypting it. However, I turned that off when I downloaded Kaspersky Full Security. Apple Genius’ told me that it’s permanently locked in target mode now. I felt my heart start pounding, it felt like I was gonna go into cardiac arrest! I said, no no please. Can you help me? Even if I have to lose everything on the Mac, please help me fix this. They said I needed to bring in the purchase receipt and / or find the password for FileVault to unlock target mode. It’s simply black with the lock symbol and one entry row, password. If you try to go into recovery mode, it doesn’t allow it. I cannot delete / erase it, I don’t have the receipt. I bought it from a seller on OfferUP! I have the record of sale, and it’s registered to my Apple & iCloud account! It has a lot of data, and I have 4 external SSD’s hooked up! I’m freaking out. I can’t lose my Mac Bc of a programming idiocricy of locking you out. It didn’t even work. When I unplugged it, it went to the Lock Screen and has remained there. I’m at wits end! Please if anyone has been through this, would u please help out a fellow human? I NEED it to work again & ASAP! I even took the back off, removed the upgraded SSD card I installed for extra memory, rebooted the computer. Guess what, it still goes to the same black screen and white lock symbol.