Use Mercurial histedit extension, this is a game changer on all operations. Works like git rebase -i but just better combined with phases. So most likely your not-yet-pushed commits are marked as draft, so you can run hg histedit.

We use this ALIAS:

histamend = !$HG histedit $(hg log -l1 -r '(draft() or secret()) and branch(.)' --template={rev})

This shows you option to drop/squash re-order/edit messages on all draft or secret commits in the current checkout branch