Thre is a couple of ways to do this. It depends on the functionality you need.
This will make the columns equal
With the Equalise switch active in the Design settings the column rows need to be coloured NOT the module.
Flick the switch in the Row settings
Design > Sizing > Equalize Columns Heights
This will make the modules inside columns equal
Add the following code to each of the Row Column Main Element areas.
There is a more detailed tutorial on this here