Randomizing sub-blocks within blocks

I was wondering if I can get assistance on randomization on DirectRT v.2006.1.0.16. I divided tasks into blocks, and there are 2 separate blocks in which I want sub-blocks to be randomized, but NOT the trials within each sub-block. How can I go about doing this? I tried playing around with the RBG values, but all I get are the sub-blocks randomizing ACROSS both of the bigger blocks, not limited within their respective bigger block.

Any help will be appreciated. Thanks!