If you are self-employed and you make over $30,000 in revenue from taxable sources combined in four or fewer consecutive calendar quarters, you need to file an HST/GST return. To do so, you would first register with the Canada Revenue Agency (CRA), and then you can submit your HST/GST return online.
This CRA webpage has more information on when you need to register for an HST/GST account:
https://www.canada.ca/en/revenue-agency/services/tax/businesses/topics/gst-hst-businesses/when-register-charge.html
This CRA webpage has more information on filing an HST/GST return:
https://www.canada.ca/en/revenue-agency/services/tax/businesses/topics/gst-hst-businesses/complete-file-return-business.html