A friend of mine is building a website for a client using Woocommerce.
For the shipping fees, he is using a plug-in provided by the postal company that calculates the fees according to the total weight of the order and the destination.
So far so good, but his client wants to add an insurance fee to the postal fee, and unfortunately the said plug-in doesn’t feature that option.
The customer wouldn’t have the choice : the insurance would be added automatically to the shipping fees.

I am not a Woocommerce specialist, but I have the feeling that adding a few lines of php could do the trick, something like :

if total < 100€ then add 1€
if total >= 100€ and total < 200€ the add 2€
etc.

The problem is that I have no idea where to add these few lines of php.

Thank you in advance