Here we have a case where the modern subject pronoun form you was replaced in the 1837 edition by the archaic subject pronoun form ye. The apparent source for the change is the otherwise identical language found in the following clause: “I know that ye believe them”. Interestingly, earlier in the verse we have a subject you that was not changed (“do you believe these things”), which suggests that the 1837 change of you to ye in “yea I know that you believe them” was unintended. As discussed under Mosiah 4:14, both ye and you can occur as the subject pronoun, although ye is considerably more common in the Book of Mormon text. For additional discussion, see under ye in volume 3.
Summary: Restore in Alma 7:17 the subject pronoun form you in the clause “yea I know that you believe them”; the 1837 change to ye was apparently prompted by the ye in the following text: “and the way that I know that ye believe them is by the manifestations of the Spirit which is in me”).