I saved to the app, it is under expired deals and no code or redeem option is showing.
Yup seems it expired on the 13th,which was the deadline for saving it on a notepad to use for a later date.
Save in the T-Mobile Tuesdays app by August 8, 2018, at 4:59 a.m. ET and redeem by August 13, 2018, at 11:59 p.m. ET to receive a code. Redeem the code in the Google Express app by August 21, 2018, at 2:59 a.m. ET to receive 25% off (up to $40) via the Google Express app.