I need to cancel the sweep app it keeps changing my bank

Look here, you can

• View your purchase history

• Cancel a subscription

• Request a refund

• Verify unfamiliar charges

• Add or remove a payment method

Subscriptions and Billing - Official Apple Support

Settings>General>Iphone Storage... scroll down to the Sweep app, tap it, then choose delete.

When done, restart your iPhone.

Regards

Giulio

EDIT: Since that app is free, there's no related subscription. I don't see how it could have "changed your bank account".