I am not familiar with Sbi Life Insurance however surrendering policies are generally the same with every company. The fastest way is to write a letter to the company, perhaps filling out a company specific form requesting to surrender the policy.
A common way is also to just stop paying the premiums. I would only recommend this on a term policy where there is no cash value in the policy otherwise the policy may not be surrendered until the cash value is exhausted.
To the best of my knowledge, SBLI or Savings Bank Life Insurance Co. only markets term life insurance. I may be wrong, but if you purchased a life insurance policy through SBLI, it is likely term life insurance and there is no surrender procedure. Term life insurance is merely cancelled or allowed to lapse. There is no cash value in term life insurance and there for nothing to surrender. Only cash value plans such as whole life insurance or universal life insurance need to be surrendered. Just call and cancel it. SBLI phone number is 888-438-7254.
A common way is also to just stop paying the premiums. I would only recommend this on a term policy where there is no cash value in the policy otherwise the policy may not be surrendered until the cash value is exhausted.