Unsure of what approach to take

[marc1n]

If you don't know anything about the password except its length then you are left with the brute force method but in your case recovering a password of 12-14 characters on this 7z hash is virtually impossible. See how many hashes it breaks per second 14 cards 3090 = 14270.2 kH/s Simply put 7z has a very strong encryption algorithm.