The Debt Collective named Sen. Chuck Schumer (D-N.Y.), Rep. Hakeem Jeffries (D-N.Y.), Sen. Maria Cantwell (D-Wash.), Sen. Tammy Duckworth (D-Ill.), and Rep. Rick Larsen (D-Wash.) as particularly responsible for the language.
I mean, that's one interpretation, but Biden's initial stab at cancellation probably wouldn't have happened without Schumer getting on board and making it less just "Warren calling for stuff she wants". Harder to dismiss it as progressive fringe when the majority leader keeps calling for it.
My interpretation is that them being "responsible" is just a list of the Democratic leaders in each chamber and the expected sponsors rather than them actually making the edit. Flood their phone lines for sure, because they're the ones who can shut it down (and arguably should have noticed and shut down without needing outside watchdogs), but I think it's pretty obvious this was a Republican insertion. Even if they didn't believe in debt cancellation, it's still a good campaign issue for them and they could just rely the courts and filibuster to block their performative efforts.