To see if you SSL version for AnyConnect is on a safe level. You want to check this first via the following website https://www.ssllabs.com/ssltest/analyze.html
You need to enter your domain name which you use to connect with the clients to logon to.
For this you need to use at lease ASA software version 9.3(2) or later In earlier versions the TLS 1.2 is not supported.
To configure the TLS 1.2, you can use 2 options. via the command line or via the ASDM.
First via the Command Line, you need to enter the following command’s
ssl server-version tlsv1.2
ssl client-version tlsv1.2
ssl cipher tlsv1.2 high
ssl dh-group group24
After you changed this you can to a recheck via the earlier given website.
If you want to set this settings via the ASDM you need to go to
Remote Access VPN > Advanced > SSL Settings
Set the version for server as for client to TLS V1.2 put the Diffie-Hellman Group to 24 most secure option which is available. At the Encryption put the TLS V1.2 to High.
When you do the re-check you will see the follow output