Don't flag for moderator attention. There is a dedicated flag pathway for migration. It goes like this:
This flag will put the question in the close vote review queue, which brings it to the attention of high-rep users and moderators who can actually carry out the migration.
That said, I would like to repeat from my comment earlier that migration is only appropriate for questions that are truly off-topic here per the Help Center's guidelines. If enough reviewers think the question is on-topic here, your flag will be rejected.
Once you have 3000 reputation points, you will be able to cast close votes; the interface is similar to the flag interface. Casting a close vote also puts a question in the review queue; once you gain the ability to vote to close, you are not usually supposed to flag questions for closure.
If you just want to guide users to ELL or make sure that they know about the site, a good option is to leave a comment saying something like
Hello! I would like to mention that there is a separate site especially for English Language Learners; it’s possible that this site would better meet your needs. You can learn some more about the differences between the two sites here: What is the difference between ELU and ELL?