Yes. Platform.sh issues a free Let's Encrypt SSL Certificate that is renewed automatically every 90 days.
Retrieve the list of certificates with:
platform certificate:list
From that list, get the CERTIFICATE_ID of the certificate you want to delete.
You can remove your custom certificate with the following command:
platform certificate:delete <CERTIFICATE_ID>
You can then redeploy and the Let's Encrypt SSL Certificate will be automatically applied.
For more information on this feature, please see the following page in the Platform.sh documentation:
https://docs.platform.sh/define-routes/https.html#tls-certificates