Following are the two solutions that can backup your Pinterest pins easily.
First one is quite popular and i think most of people already know it. It is easy and fast and i think if you are not a marketer or a power user of Pinterest the free plan is ok but if you want more than just back up of your pic pin-s then you can try their other plans.This tool works on firefox browser so better install it if you don’t have it and follow the installation instructions as per described on the their website.
This tool will work in any browser and is released under the MIT license. All you have to do is install it to your browser and login Pinterest then after clicking the pinback it tool you can export them as per your wish..whether group board or individual one. This will be saved in a html format to your pc.