You will need to complete the application form and submit it at the Visa Application Center for Greece in Sri Lanka - Colombo. For the location click here
Under the new visa system link implemented by all Schengen missions in Sri Lanka as of November 2, 2015, all VIS visa applicants must submit their application in person in order for their biometric data (10 fingerprints and digital photo) to be taken.
Please note that appearance in person for all applicants regardless of age is mandatory for biometrics. Subsequent Schengen visa applications within 5 years may be submitted through authorized representative only if the applicant has a Greek visa VIS.
Visa applications should be lodged no later than 20 calendar days prior to departure. Applications may be submitted at the earliest 3 months before departure.
For further details, please consult the following notice from the Embassy of Greece: