Hey aravindh, 

CLAT as you know is also called as Common Law Entrance Test conducted by National Law University , Odisha , Cuttack for admission year 2019-20. It will be admisnisterd offline and the exam is scheduled for 26th MAy 2019. The last date for registration is 15th April 2019. It has been extended to 15th april. 

As far as I know, there is no option to apply again from same user id and password. But also , the half filled form can not be submitted , if it is submitted you can proceed only if you have filled all important details, then only you can proceed to final submission. 

according to the instructions :

• After regestering on CLAT website using details like phone number and email ID upon which youll get OTP for validation. Once validated, you can login through mobile number and the password at time of registration. 
• Form filling should be done carefully, for once the form is submitted , you dont have portal for correction. 
• Name of candidate and Parents Name must be spelt correctly in application form as it appears in certificate and marks card. IF alteration is found , it leads to disqualify in candidature. 
• No alteration or editing can be done after succcesfull submission or final submission of form. 
• Information regarding caste, preference of NLU's as well as centre of entrance test can not be changed in any circumstances. 
• Information provided must be true to the knowledge and must be correct , if found otherwise , the admission might get cancelled. 

If you have not filled up and have done final submission, then you have choice of editing the same application. If not, I am sorry but you can notapply again from same userid and phone number. You will have to do from any alternatives. Kindly check once , if the submitted form was asked for final submission or  you have chance to do final submission. 
For further details , you can also refer this link : https://law.careers360.com/exams/clat 
 you can also contact them on this id : clat2019@nls.ac.in ; +919741521069, 9482567257 (bengaluru) ; +918480718979 ( odisha) 

Hope it helps, 
Good Luck.