It always at the right top of engineering data. For ANSYS Workbench 15, the table of properties is at Row 9,. Here I attached my picture.

See in the first figure 

I started creating new material and I added Alternating stress mean stress

In the right side top corner table of properties is there( ref untitled2) 

In the table add a value and press enter then next row will come (ref untitled3)

in this way you can create table

If on right side top table of properties is not there (untitled4), then go to view and highlight table (untitled5)

then table of properties option(untitled6) will come 

all the best

Use MP command.