You can follow these simple steps:

1. Click on the Investments section (bottom of the screen).

2. Click on the Investment Summary Card (where it shows your current amount).

3. Click on the "SIP" Tab. Here you will be able to see the list of funds in which SIPs have been set up. 
4. Click on the 3 dots beside the SIP you wish to stop or modify. Select Stop SIP or Modify SIP

Modify SIP allows you to change the date or/and the amount that will be invested from the next SIP onward. When you make changes to the SIP, the old SIP is stopped and a new one is set up with the desired changes. This won't affect your existing investments and the changes will be done only for your future SIP payments.

You can Modify or Stop the SIP until 1 day before the SIP date. For example, if the SIP is on 15 Jan, then it can be stopped/modified until 14th Jan.