Scribe 2 of 𝓟 initially miswrote the word teach as preach. He immediately crossed out the incorrect preach and wrote the correct teach inline. Both words are, of course, semantically related; in fact, in some instances in the text, preach and teach are conjoined (as in Alma 23:4: “to preach and to teach the word of God among them”). Thus it is not surprising that there are other instances in the history of the text where teach and preach have been mixed up:
In each instance, we let the earliest textual sources determine whether the word is teach or preach.
A similar example where scribe 2 of 𝓟 deleted a word that he had expected, but which was wrong, is found later on in Alma 8, namely in verse 10. There he initially wrote “wrestling with God in mighty power”; but then he immediately crossed out power and wrote inline the correct (and visually similar) prayer. It’s possible that scribe 2 was thinking of Jacob wrestling with God (as described in Genesis 32:24–32).
Summary: Maintain the verb teach in Alma 8:4 and prayer in Alma 8:10, immediately corrected readings in 𝓟.