If you previously had a Stripe account linked to your SimplePractice account before setting up Online Payments, you will still have access to that previous account for record-keeping purposes only. This means you will have access to two Stripe accounts, but you'll only be managing transactions and payouts moving forward from your integrated SimplePractice experience. This information will not be reflected in the separate Stripe dashboard associated with your previous account.
Only you've enabled the integrated Stripe experience in SimplePractice, you'll need to use the Payout reports and Card Transactions report to manage your payouts and transactions. This cannot be done or accessed from your old Stripe dashboard.