Hi andre.frost,
This documentation will give you the steps to follow:
http://www.cisco.com/c/en/us/td/docs/security/vpn_client/anyconnect/anyconnect40/administration/guide/b_AnyConnect_Administrator_Guide_4-0/configure-vpn.html#ID-1428-00000555
AutomaticCertSelection
o If you use the AutomaticCertSelection set to false the user should be presented a drop down list with the certificates he can use
o If this option is set to true, the system API returns the certificates in it's own order

Having the API doing their own check order is not fully recommended since this one could select the wrong certificate.
On the same document you have the option of using certificate matching which is going to set a criteria to be checked on the certificate.
Hope this info helps!!
Rate if helps you!!