Here is what you can do to integrate MSG91 SMS Gateway:

Go to Configuration -> SMS. Choose "Custom" SMS Gateway and enter the following inputs:

Sender Id Param: sender
Sender Id: Your sender Id
Receiver Param: mobiles
Message Param: param
Multiple Receiver: true
Prefix: 91 or blank if you are already storing 91 with mobile numbers
Max SMS in Single Queue: 200-500

Once completed, make sure you have setup cron job (For Regular or Extended CodeCanyon License) as mentioned here.

No cron job is required for SaaS Version.