How do I write code to perform a function on dynamic cell range?

Hello,

I am a vba novice, and need help to figure out a simply issue.

I am creating an inventory management userform, and I aim to include a code to give notification (MSgBox) whenever 'Reorder level units = Available inventory units ".

Attachment 29216
In the image attached, my code works only for the first Product item in cell Row 2, but I am unable to get it to work on subsequent Products items down the rows in a dynamic way. Please note that cell range here is dynamic (Product items are added routinely).
I have tried .autofill and other ways on the internet, but I just can't get it right. Please help. Thanks in advance.