The Book of Mormon text systematically uses the two-syllable doeth for stressed forms of do but doth for the corresponding unstressed verb form. Except for one case, this corresponds with using doeth as the main verb form and doth as the auxiliary verb form (for the one exception, see under Alma 3:19). Here in Moroni 7:8, the 1837 edition changed the original doeth to doth, an error that was nonetheless copied into both the LDS and RLDS textual traditions. The correct doeth was restored to the LDS text in 1879 and to the RLDS text in 1908. For further discussion of the competition between doeth and doth, see under Mosiah 4:18.
Summary: Maintain in Moroni 7:8 the original two-syllable doeth since here do occurs as the main verb and is stressed.