To amend something to a selected (unpushed) commit, use the Modify option. This will start an interactive rebase and stop after the selected commit. Perform the modification and then click Commit/Continue toolbar button, select Create Commit and in the Commit dialog select the Amend last commit checkbox. Now click again Commit/Continue toolbar button and select Continue Rebase. If you want to To abort the rebase going Modify command and go back to the previous state, use the Abort toolbar button.
For the split command, the interactive rebase stops after the selected commit, a
As stated above, you may perform a couple of modification operations already using specific commands, e.g. reordering commits by drag and drop. They will be performed immediately. If you have to make multiple changes at once or the immediate commands aborted because of conflicts, you should rather use the Interactive Rebase.
To start the interactive rebase command, select the first commit that should be changed. In the occurring Interactive Rebase dialog you will be able to perform similar operations like in the Journal directly, e.g. squash commits, reorder using drag and drop, edit commit messages, but they only are performed when clicking the Rebase button. In case of conflicts, the rebase will stop (like a normal rebase, too). After solving the conflicts, click the Commit/Continue toolbar button and select Continue Rebase. To abort the interactive rebase and go back to the previous state, use the Abort toolbar button.