Not sure how. The email I received mentions that you can opt out as defined in section 11. When you click the link it just opens the app and gives you no further information or options.

Update: I reached out to customer service. They gave me the same broken link. It just leads to the home screen in their app. They're "looking into it."

Feels illegal to me. Very disappointed in what had otherwise been a decent service.

Double update:

You have to physically mail a letter to them. Fuck them:

"Existing customers who agree to this as a terms update may opt-out by sending an opt-out notice within fourteen (14) days (the "Opt Out Notice") of agreeing to such updated terms. The Opt Out must be mailed to USM Inc., Attn: Legal/Arbitration Agreement Opt Out, 295 Madison Ave, 6th Floor, New York, NY 10017. Include your name, address, phone number(s), account number, email address, and a statement signed by you that you wish to opt out of the arbitration provision. This is the only way to opt out of this arbitration agreement."