Flashing will wipe all internal storage. Save your photos and files.
Some of the key features that custom firmware for the T337A and similar devices might include are: t337a firmware
If the tablet won't boot, power it off, then press and hold Volume Up + Home + Power buttons simultaneously until the recovery menu appears. Use the volume keys to select Wipe data/factory reset and the Power button to confirm. 4. Technical Constraints Flashing will wipe all internal storage
Look for the specific SM-T337A build (usually Android 5.1.1 Lollipop). power it off