Are you asking when YOUR tax return was filed? If you mailed it then you are the only one who knows when you took it to a mailbox, unless you have a receipt from UPS or certified mail, etc.
If you e-filed, you received several emails about e-filing. And you can check your e-file status using the e-file status lookup tool. Or look in your account and see what it says about whether your return was accepted or rejected.
https://turbotax.intuit.com/tax-tools/efile-status-lookup/