The DND app itself sends out a formatted SMS to 1909. If you copy the format you can manually send an SMS as well.
2.4.1
As per the current provisions, every access provider has setup a mechanism for registering complaints of its customers regarding receipt of UCC through voice call or SMS to toll free number 1909. For complaint through SMS, customer has to send SMS "COMP TEL NO XXXXXXXXXX; dd/mm/yy; Time in hh:mm; short description of Unsolicited Commercial Communication" to 1909, where XXXXXXXXXX - is the telephone number or header of the SMS, from which the UCC has originated.
https://trai.gov.in/sites/default/files/Consultation Paper on UCC3_8_12.pdf
You can even call 1909 and raise a complaint IINM.