There is no way to request the third stimulus check at this time ... even if the 2020 return is filed they may not put out a check based on that return. Just like the first 2 checks, if you don't get any or all of the third check in advance you will need to apply for it on the 2021 tax return you file next year. And FYI they are still issuing third stimulus checks and will be for some time now.
