Factory resetting a Galaxy Tab 3

I haven't used my Galaxy Tab 3 in ages and would like to use it again, but it's not working as it used to. I would like to perform full system restore, but I'm having real problems.

Last month:

I press the On / Volume up / Start buttons to get to MANUAL MODE.

It gives me an option to do a factory reset, and says to use the volume buttons to get to this option.

I press to go down and it skips over the reset option, meaning I can't do it.

Today:

I press the On / Volume up / Start buttons and it crashes on MANUAL MODE saying:

-- Applying Multi-CSC...  

Applied the CSC-code : BTU  

Successfully appled multi-CSC.  

How do I do a factory reset in another way?