LEGO MINDSTORMS EV3 Can't find MyData Block
EV3 software comes in two varieties, Educational and Home. The Educational version has a few blocks that do data operations that make sense in a science class.

Both versions are downloadable from Lego for free.

I think the MyData block is actually the data logging block.  It looks like this:



To get this block for use in your programs, you would need to download and install the Education version of Mindstorms.