Bootstrap 3 with Sage 8.5.1

Hello everyone,
I want to know the steps to use bootstrap 3 instead of 4 with Sage 8.5.1.

Thanks in advance

You need to delete bootstrap4 in bower.json and install bootstrap 3 like you want.

Could you show me the exact code to do this

I think that I should do some changes in files _grid.scss… etc in components folder as well?