To pledge your shares, 

1. Tap your profile picture>Funds>Pledge.
2. Choose the holdings you wish to pledge and enter their quantity.
3. Check the estimated margin you’ll receive and tap Pledge Now.

You will then be redirected to the CDSL pledge authorization page. After this, authorize the pledge request using the OTP received on your registered mobile number.

Note: After you’ve successfully pledged the shares, the margin will reflect in your trading account before the beginning of the next trading day.