The original text here is morphologically ambiguous. One way to interpret the conjunctive series of verbs is that we have a perfect form (“have broken bread”) followed by two simple past-tense forms (“and blessed it and gave it unto you”). The alternative reading is that we have three conjoined past-participial verb forms, as if the text read “have broken bread and have blessed it and have gave it unto you”. This is how the text was interpreted when it was edited (in 1907) for the third printing of the 1905 LDS missionary edition. Since “have gave” is nonstandard, the gave was edited to given. The subsequent LDS text has continued with this emendation. See under 1 Nephi 5:8 for further discussion of this kind of editing of conjunctive verb phrases as well as the existence of “have gave” in the original text.
This alternative interpretation is probably correct, given the other references in 3 Nephi to the Lord’s sacrament:
In these three cases, the auxiliary verb (shall, should, or did ) requires that any following conjoined verb take the infinitive form. Similarly, the probable interpretation for 3 Nephi 18:6 is “have broken bread and have blessed it and have gave it”, which means that in the standard text the grammatical emendation given should be accepted. The critical text will, of course, restore the original gave, no matter which interpretation is accepted.
Summary: Restore the original gave in 3 Nephi 18:6; in this passage, the gave appears to be the nonstandard past-participial form for the verb give; usage such as “have gave” occurred in the original text and will be restored whenever the earliest textual sources support it.