The correct reading here is the plural noun phrase the heavens. In the printer’s manuscript, scribe 2 originally wrote simply Heaven, but virtually immediately he corrected it to the Heavens (the correction is written with slightly heavier ink flow). The 1830 edition also reads the Heavens, which argues that 𝓞 read this way. Interestingly, the 1905 LDS missionary edition changed the plural the heavens to the heaven, by accident, it would appear. This secondary reading continued in two subsequent LDS editions (the 1907 vest-pocket edition and the 1911 large-print edition), but the 1920 LDS edition restored the correct the heavens to the LDS text. For further discussion of the competition between the heaven and the heavens, see under 3 Nephi 26:3.
Summary: Maintain in 3 Nephi 28:36 the plural noun phrase the heavens, the 1830 reading as well as the corrected reading in 𝓟.