Not to worry, I'm sure we can help you out here. When you first start a Shopify store, a placeholder PayPal account is set up for you under the email account you used to sign up. It sounds like you've gone to Settings >Payment Providers and added PayPal, then added your own PayPal account? If the PayPal account was changed after the sales were made, the funds may be in the placeholder account. You would just need to complete the set up of that account to access the funds! Could you check the email account listed as the account owners and see if there are any emails from PayPal asking you to complete the account set up? If you can find that and complete the setup, you should see the funds from the first order in that account.
Could you let me know how you get on so I'm sure this has been resolved for you?
Social Care | help.shopify.com