First, fork the gentoo/gentoo github repo, to your USERNAME/gentoo repositrory. And then clone to your local machine.
You also need to have gnupg signature and register to make pull request on github. You can search how to on Google.
Below is the big flow of ebuild version bump.
$git branch test $git checkout test $cp 1.ebuild 2.ebuild $vim 2.ebuild $repoman manifest $repoman full -dx $git add 2.ebuild Manifest $repoman ci $git rm 1.rebuild $repoman manifest $repoman ci
*There must be 2 commits, 1 is for addition, and the other is for removal.