See:
How do I explain to my mother to AES decrypt "71TjQQYPkadCq8qUA6Lqt7FhUBEjPSzgDSbBA6spbtD/j8v3JXp9Vpco0H8rS/TK2/IOMS0aHF5QIyLihGuP2dSgdoKdyDrb82O72tNPdT4=" and ensure to type it out correctly?
Birthdays and anniversaries everyone remembers, and with 24 seed words you can shift it with up to 8 dates. Never said it's unbreakable, but it's not easy to break either, it gives you plenty of time to react in case of theft and it's simple enough by knowing the dates to do it by hand.
You didn't get it.
First, you could just write that down.
"Dear mother, decrypt the following thing by pasting it into the software called XXX on my PC: ..."
Second, that is not what i wrote.
Your secret data you have used for the shift cipher were some dates.
You could use exactly these dates (the secret information) as a key in an AES cipher. That would be already way more secure than your approach since it wouldn't leak anything about the plaintext at all.
And when decrypting, that is exactly the same effort (Taking secret info X and doing Y).