Here in the printer’s manuscript, scribe 2 wrote the verb declare as deliver both times. Oliver Cowdery, in proofing against the original manuscript, corrected both to declare. The 1830 edition, independently set here from the original manuscript, also has declare in both instances. So the original manuscript undoubtedly had declare, not deliver. The visual similarity and semantic compatibility of the two words led scribe 2 to make this substitution.
Elsewhere in the text there are 20 references to delivering a message but 111 of declaring a message. Either verb is possible here in 3 Nephi 21:2. In each case, the critical text will follow the earliest reading, thus declare twice here in 3 Nephi 21:2.
There are two other examples in the early text where deliver and declare were mixed up, a momentary one immediately corrected by scribe 2 of 𝓟 and a permanent one by the 1830 typesetter:
In the second case, the original declare was replaced by deliver apparently under the influence of a preceding deliver in the text (see under Alma 5:1 for discussion).
Summary: Accept the two occurrences of the verb declare in 3 Nephi 21:2, in each case the corrected reading in 𝓟 and the reading of the 1830 edition.