e.g. if you have your branch `feature-1` and want to rebase it on `main`, then you would do `git checkout feature-1; git rebase -i main`
Git will then switch to main (that's "ours" now) and then it will replay the changes from `feature-1` on top of it (that's "theirs" now) - like cherry-picking all your commits, but in sequence (and not actually merging them in `main`)
This is exactly the reason that git is hard. Its abstractions are so leaky that you'd think it's interface is designed to be a sieve. I really like the underlying model git uses, but the actual CLI does a terrible job of providing mechanisms to use it to the point where you have to pay far too much attention to the internal model to be able to avoid footguns. It's an indictment of a poor API when the best way to figure out how to do something isn't to search the docs but to figure out how to express the thing you want to do as an operation on the underlying model and then Google that to find the invocation that happens to map to that operation (and half the time, it's not even it's own subcommand; it's just some obscure flag to a grossly overloaded subcommand like `checkout`).