Connect the Samsung Galaxy Tab S2 to the computer using the USB cable. Copy the custom ROM zip file over to the internal storage SD card. Unplug your Tab S2 from the computer. Boot the Galaxy Tab S2 tablet in recovery mode. Tap over the ‘Backup’ option from the recovery mode menu. Tap in the ‘Install’ option from the recovery menu.
Download Odin for Samsung Galaxy Tab 3 8.0 SM-T310. Now, you have to download root Zip files (Odin 3) to your computer. After downloaded, unzip it/ extract it. After unzip you can see , Odin3.ini, tmax.dll and zlib.dll files. Step 3, Bring your Tab and turn it off by pressing power button. Make sure whether your Tab is off before going to Step 4.
In ODIN, uncheck the Auto Reboot box. This is because the OS will re-flash the stock recovery upon reboot. Leave everything else as it is. Click the Start button in Odin to start flashing the recovery. Once done, you should see a PASS message at the top-left in Odin. Disconnect the tablet and reboot to TWRP.DFA2nX.