You have to attach a certificate of your work experience provided by your field work agency. Here is the sample of the certificate.
TO WHOM SO EVER IT MAY CONCERN
This is to certify that Name of the volunteer/trainer, who is doing MSW from IGNOU, has volunteered at Name of the agency from date to date.
The beneficiaries at the agency greatly benefited from his/her experience. Our agency wishes all the best for his/her future.
Name of the project coordinator/authorized person
Signature with seal