There is no such thing as filing quarterly tax returns, even if you are a sole proprietor. You file ONE tax return---one Form 1040 -- per year. You can make estimated quarterly tax payments to avoid a big tax bill at tax time.
If you want to send in quarterly payments:
https://turbotax.intuit.com/tax-tools/calculators/self-employed/
https://www.calcxml.com/calculators/self-employment-tax-calculator (non-TT site)
https://www.irs.gov/pub/irs-pdf/f1040es.pdf
https://www.irs.gov/payments