You can edit TdgssUseConfigFile.xml (found in tdgssconfig.jar in the ...\tptwizard\jars folder) to either designate LDAP as default mechanism or change its rank.
Save a copy of the jar file just in case. Use the jar.exe utility from the JDK to extract the xml file and then to update the jar with the edited version.
Thanks Fred, I was not having access to change/save jar file in LDAP environment but I am able to see xml code where you meant changes.
I found below method and using it on login screen harpreet
Teradata host= hostname/LOGMECH = 'LDAP'