I can see the form in the list of forms to be filed but note the following:
Do not file Form 1120-S for any tax year before the year the election takes effect. If the corporation (entity) is now required to file Form 1120, U.S. Corporation Income Tax Return, or any other applicable tax return, continue filing it until the election takes effect.
See https://www.irs.gov/instructions/i2553#idm139855003318528
