How do you get a trust fund that was left in an account and only you can redeem the funds when you reached 18 years of age but was lost and have no records of the trust fund being in the account?

If you have a trust fund, some record of it exists somewhere. I do not believe that every record was lost. Find the record. If, however, there is absolutely no record remaining anywhere, then there is no way to prove that you own this money and you will never be able to obtain it.