The source for Oliver Cowdery initially writing the word know in the printer’s manuscript is undoubtedly the clause “and also we know of their surety and truth” that is found in the preceding verse (Mosiah 5:2). Oliver’s crossout of know here in verse 3 appears to be virtually immediate; there is no change in the level of ink flow, and the immediately following text was written inline. And, of course, the actual verb for this sentence (have) occurs after the long prepositional phrase (“through the infinite goodness of God and the manifestations of his Spirit”); thus the use of know earlier in the sentence is impossible.
Summary: Maintain in Mosiah 5:3 Oliver Cowdery’s virtually immediate correction in 𝓟 (his crossout of the verb know).