Please fill out the fields below so we can help you better. Note: you must provide your domain name to get help. Domain names for issued certificates are all made public in Certificate Transparency logs (e.g. https://crt.sh/?q=example.com), so withholding your domain name here does not increase secrecy, but only makes it harder for us to provide help.
Access your website in your favorite (S)FTP client or use your web host's online file manager to navigate to the wp-content/plugins subdirectory of your WordPress installation, then delete the better-wp-security directory. This will remove the plugin and should allow you to login to your WordPress admin again.
This plugin shouldn't be necessary to get your admin interface to load over HTTPS; WordPress is perfectly capable of doing that on its own. But if you want to reinstall and continue to use it anyway you will need to get further help from the plugin's forum.