If you want to disconnect your PayPal account from your Splitser account, go to Account > Payment methods > PayPal. Here you follow the link to the settings of your PayPal account. There you can revoke the permissions granted to Splitser. It may take a few minutes before the unlinking is visible in the app.
If you can no longer access your PayPal account, and you want to unlink your PayPal account, send mail to info@splitser.com.