There are many ways to set column widths in flexbox but you do really need to take some time and study the methods as there are hundreds of good resources out there
As a quick summary you can control widths in many ways:
You could simply give one column a width and the other column flex:1 0 0% and then the second column fills the rest of the available space.
You could set one column to flex:2 0 0% and the other to flex:1 0 0% and that means the first will take up twice as much room as the second assuming that there is no fixed width content.
You can use combinations of min and max width and many variations of the flex shrink and grow properties to achieve the desired result.
I’m on a mobile at the moment so can’t offer code but I suggest you try yourself first and then I’ll be back later this afternoon with full code if needed