The University of Houston–Victoria website explains that when omitting part of a quote in which the original author used ellipses, the writer is to use ellipses within square brackets. (MLA style)
Ellipses in Work that Includes Ellipsis
If the original work includes ellipses, include your ellipses in brackets [. . .] to distinguish between yours and the author’s.
Original: I had an experience I can't prove, I can't even explain it, but everything . . . tells me that it was real. I was part of
something wonderful, something that changed me forever; a vision of the Universe that tells us undeniably how tiny, and
insignificant, and how rare and precious we all are.
Parts Omitted: “I had an experience I can't prove, I can't even explain it, but everything . . . tells me that it was real. I was
part of something wonderful, [. . .] a vision of the Universe that tells us undeniably how tiny, and insignificant, and how rare
and precious we all are” (Contact 231).
Website:
https://www.uhv.edu/university-college/student-success-center/resources/e-p/ellipsis-use-in-mla-style/