You can use the following commands, if you want to do it in a shell:

racadm set idrac.webserver.tlsprotocol 2

If you want to do it in the web UI, navigate to Overview > iDRAC Settings > Network, then select Web Server and TLS Protocol.

there are 2 ports listening 443 and 5900. For web server 443 already changed to TLS 1.2 as per the method mentioned below but port 5900 for virtual console there is no option. Please check if we can move this port to TLS 1.2 or it is not supported.

You can find the manual here: 

https://topics-cdn.dell.com/pdf/idrac7-8-lifecycle-controller-v2616060_release-notes_en-us.pdf

I don't see that as an option.