The way you do it is to - BOOM! - expand the Court to 13 on Day 1 of the next Biden administration, if Democrats also have both houses of Congress, nuking the Fillibuster if necessary, but delay it’s effect until September 2026.
Then, go to Republicans and give them a choice. Either we can reform the SC and institute meaningful reform, or Republicans can watch Biden appoint four judges in their 40’s to lifetime appointments, and they can wait until they have the Presidency and both houses of Congress to make a tit-for-tat response. (Biden’s appointments would only be subject to those term limits if the amendment passes before he makes the appointment.)
We can do a lot in an amendment, including instituting term limits, a firm code of ethics, a better process for confirmation where the Senate can’t just ignore an appointment, and formally fixing the size of the SCOTUS to match the number of appellate courts.