UPDATE:
TLS to TLS conversion is available from version 1.7.0.
The command line to configure TLS to TLS conversion looks like this:
RebexTinyTlsProxy.exe -TLStoTLS -TLS10:TLS12- 443:httpbin.org:443 -c cert.pfx#password
Please note that you may need to specify the -SNI option as well:
-SNI name Server name for outbound TLS tunnel (SNI extension).
By default, the SNI received on the inbound tunnel is used for the outbound tunnel as well. For example, if you access the proxy using localhost the SNI for outbound tunnel will be localhost, which can be (often) rejected by the target server. To use correct SNI for outbound tunnel, specify the -SNI option (for example: -SNI httpbin.org).
Please also note that for TLS to TLS conversion you need to use a valid certificate for the proxy.