Today I had to merge changes from one repository into another. Let’s assume you want to merge beta into alpha.

Operations are performed in repo alpha:

git remote add beta_repo
git fetch beta_repo
git merge beta_repo/master

In this case, beta_repo is the name you pick for remote.

If you just need to cherry-pick a certain commit from beta you can omit the last step and replace it with the cherry-pick.

More on the topic of remotes: