Finding duplicate values

Hello.
I am facing some problem to identify the duplicate entries in my recruitment database sheet, sometimes the some candidate details are repeating.

Kindly help me to check the following feilds to verify the database with script.

1) Candidate Name
2) Date of Birth
3) Cellphone Number

If the above field values are repeating in my detabase some alert has to popup, so that I can avoid duplicate entries,

Please check the attached file for more details

Kindly help me,

Regards
Sagar