Inspiron 5568 - boot issue - Please HELP!

Hi... Was told to check out this thread to try and resolve my boot issue. This is what the screen says when booting "Operating system loader has no signature. Incompatible with SecureBoot. All bootable devices failed Secure Boot verification".

Tried in BIOS to switch from Legacy to UEFI as the thread recommended however UEFI was already selected.

Wondering what else can be done to fix this.... it's all new to me :)