In the that- clause for this sentence, both manuscripts have the present-tense swear, but the sentence as a whole is clearly in the past tense. Thus the correct reading is the past-tense homophone sware. The 1830 compositor correctly set sware, but there has been a tendency in the textual history to revert to the incorrect swear (in the 1841 British edition and in the 1874 RLDS edition), perhaps because the preceding verse uses swear: “will ye swear unto me that ye will be faithful unto me in the thing which I shall desire of you” (Ether 8:13). The 1920 LDS edition restored the correct sware here in verse 14, but the RLDS text has retained the reading in 𝓟, swear. The critical text will, of course, accept the past-tense sware. See under Enos 1:14 for further discussion of the competition between swear and sware (as well as swore) in the history of the text.
Summary: Maintain in Ether 8:14 the past-tense form sware since the context here requires the past tense.