It's a very lenthy task
First you have to download the source code of this repo and you have to open each portfolio and take the screenshot and save with the same name as in json data or you can save with any order but then need to change screenshot name in json data ,
it will be easy for the portfolio which are made only through html , js , css but for react and other tech stack you need to run it !
comment on this issue will assign you!
If you are able to finish this task then only comment , in return I will share more resources with you!