Here are the steps to do it:
# clone the original repository
git clone <url>
# Create the second repository on your server
# once the repository is created add the second remote
git remote add odoo12 <new url>
# upload the code to your new repo
git push odoo12 --all
If you are using GitHub you can simply fork the project…..
solved How to migrate an odoo 11 app to odoo 12 successfully? [closed]