Copy and paste this snippet into a flow to get started.
It’s a tricky problem that took more steps than I’d like, but it should work for you.
This toggle explains how the flow works, if you're interested.
Essentially, this snippet takes a CSV with two columns, as you described, and splits the values into two separate tables, one for each column. Then it splits the “a,b,c” values into three separate columns. Then we can flip the tables on their side so we have
We do these steps for both columns.
and then we just stitch the two separate tables back into one, using a Combine Tables step.
Does this work for what you need?