Guide

1. Open Sourcetree and go to the repository.

2. In the history view, find the commit you want to squash into. Right-click one commit before the oldest one you want to squash into and choose 'Rebase children of <commit> interactively…'

3. The 'Interactive rebase' window will open. Leave the top commit and change the next ones.

4. Click 'OK' to finish the squash.

5. Sourcetree will perform the rebase and squash the commits.