Here the typesetter for the 1906 LDS edition shifted the adverb up to a later position in the sentence, from after arose to after stood. He seems to have been influenced by the placement of the up earlier in the verse: “and he commanded them that they should arise and stand up upon their feet”. The 1906 edition never served as a copytext; thus all subsequent LDS editions follow the original placement of the up in this sentence. Of course, either reading is theoretically possible here, so the critical text will follow the earliest reading, with up after arose but not after stood. For another variant involving the occurrence of up after stood, see under Alma 36:8.
Summary: Maintain in 3 Nephi 20:2 the earliest extant reading with its use of up after arose but not after stood.