If you are asking for Tax Return Preparer phone number then you can search it on https://www.incometaxindia.gov.in/Pages/tps/trp-details.aspx#map and locate TRP at your area. Moreover if you want to be a TRP then it's allotted after passing an examination and training conducted by ITD time to time. However from a very long time, no such training/exams have been conducted.
Currently you can't apply for TRP because there are no current batches proposed by ITD for conducting any exams or training. Better would be practice with any CA or any Income Tax Practitioners so that you can learn to file ITR of people as a freelancer.