How to randomly split respondents into different blocks, depending on certain conditions.

Dear all,

I am struggling to do a conditional random split. I am trying to develop a survey for 4 products; A,B,C and D. I am only interested in respondents who have purchase the products recently, so first I screen them for their purchase frequency.
Example:
How often do you purchase each product?
Frequently Sometimes Rarely Never
A
B
C
D

I created four different blocks each one contaning questions related to each product (A,B,C and D); namely _Product A questions, Product B questions, Product C questions, and Product D questions_.

I now need to randomly assign them to a block, but only if they have purchase the product at least sometimes(sometimes+frequently). This means that if someone purchases product A and D frequently or sometimes, they should be randomly assigned either to block A questions or block D questions.

Thank you all for the help!!! 😀