According to the proforma produced by the MHTCET website for 2019 , it is refer to the Commissioner & Competent Authority, State Common Entrance Test Cell, Mumbai. So according to the proforma you will have to submit to the above mentioned office. Now the location of the office are available in internet.

I will suggest if you can , call or contact the enquiry numbers provided in the website of the above mentioned office & get connected and discussed about the submission regarding thing. I hope they will guide you the most prominent way for the submission of the form.

Hope my answer helps you. Wish you all the best for your future endeavors!