Heck, you could go as far as you wanted with it - retirement Steve talked a guy out of a robbery that caused some guy to join SHIELD years later. That’s a really contrived example, but I believe there is a theory that is basically every decision spawns multiple new dimensions - you could go as far as you want. Not that I’m hoping they go so crazy, but we could easily get more than what we “know” about.So I just want to know how many variants they have to fix from the events of Endgame. My guess is four: Loki's escape with the Tesserac, Thanos dying before he ever gathered the Stones and caused the blip, Nebula killing her earlier self, and Steve Rogers going back and living out a life with Peggy Carter because of what things were affected by Peggy's different path.
Of course, they also could be trying to stop Thanos from destroying the Stones since according to the Ancient One not having them opens our dimension to forces that would tear apart the Universe.
The first two seem the most likely since they both have to do with the Stones (well, the trailer tells us outright the Loki one is involved); the second two could be argued away as relatively unimportant, though if you take the "it's A Wonderful Life" approach, either one could change everything; the last one could be the most intriguing and be leading to all sorts of chaos for the Avengers et al,