Remove vocals from track

If its already mixed, that's like trying to take the eggs out of a cake that is already baked. If you can't have access to the multitrack session there is little you can do unless you mixed an instrumental version as well. If you have an instrumental, splice it into the track at the right point and replace the vocals.

Having access to the multitrack version means going into the protools session and punching in on the vocal. I assume you have Logic or you wouldn't be here. Load the instrumental and the mix onto 2 separate tracks in Logic, both starting at the beginning. Mute the instrumental go to the part you need to replace. Cut and mute the mix at that spot. Cut and unmute the instrumental at that point. Record what you need and match it to the sound of the original vocal in the mix (good luck). Go back to the original mix after the part you want to replace.

Yes. Load the instrumental and the mix onto 2 separate tracks in Logic, both starting at the beginning. Mute the instrumental go to the part you need to replace. Cut and mute the mix at that spot. Cut and unmute the instrumental at that point. Record what you need and match it to the sound of the original vocal in the mix (good luck). Go back to the original mix after the part you want to replace. Or load the instrumental into logic and re-record the entire vocal.

How was the song recorded?

Did you record it in Logic with the instrumental on one track and the vocals on other tracks?