I guess you ask for this reason
HTTPS is enabled on all websites by default. However, the default certificate is self-signed, meaning browsers will show a security warning.
You can install your certificate using the SSL/TLS section in your control panel. For more information, see this article.
Additionally https://infinityfree.net/support/cannot-use-or-have-problems-using-lets-encrypt-or-sslforfreecom/