Resolve merge conflicts

Re: <https://github.com/grahamperrin/freebsd-doc/tree/commercial> I need 
to resolve merge conflicts. Visually:

<https://i.imgur.com/6eZo8pP.png>

> … You can resolve merge conflicts using the command line and a text 
> editor. …

It's so long since I did this, my mind is nearly blank. Can someone help?

Thanks. My config:

% git -C /usr/doc config --list | sort
branch.13.2-RC4.merge=refs/heads/13.2-RC4
branch.13.2-RC4.remote=origin
branch.13.2R.merge=refs/heads/13.2R
branch.13.2R.remote=origin
branch.2023q2.merge=refs/heads/2023q2
branch.2023q2.remote=origin
branch.advocacy-myths.merge=refs/heads/advocacy-myths
branch.advocacy-myths.remote=origin
branch.beastie-theme-en.merge=refs/heads/beastie-theme-en
branch.beastie-theme-en.remote=origin
branch.bug-267176.merge=refs/heads/bug-267176
branch.bug-267176.remote=origin
branch.bug-270229-gpl.merge=refs/heads/bug-270229-gpl
branch.bug-270229-gpl.remote=origin
branch.bug-270338.merge=refs/heads/bug-270338
branch.bug-270338.remote=origin
branch.commercial.merge=refs/heads/commercial
branch.commercial.remote=origin
branch.d39560.merge=refs/heads/main
branch.d39560.remote=origin
branch.events.merge=refs/heads/events
branch.events.remote=origin
branch.main.merge=refs/heads/main
branch.main.remote=origin
branch.patch-1.merge=refs/heads/patch-1
branch.patch-1.remote=origin
branch.patch-7.merge=refs/heads/patch-7
branch.patch-7.remote=origin
branch.releng/12.4.merge=refs/heads/releng/12.4
branch.releng/12.4.remote=origin
branch.status.merge=refs/heads/status
branch.status.remote=origin
core.bare=false
core.filemode=true
core.logallrefupdates=true
core.repositoryformatversion=0
credential.helper=store --file /usr/doc/.git/.git-credentials
remote.freebsd.fetch=+refs/heads/*:refs/remotes/freebsd/*
remote.freebsd.fetch=+refs/notes/*:refs/notes/*
remote.freebsd.pushurl=git@repo.freebsd.org:doc.git
remote.freebsd.url=https://git.freebsd.org/doc.git
remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
remote.origin.gh-resolved=base
remote.origin.url=https://github.com/grahamperrin/freebsd-doc.git
remote.upstream.fetch=+refs/heads/main:refs/remotes/upstream/main
remote.upstream.url=https://github.com/freebsd/freebsd-doc.git
user.email=grahamperrin@FreeBSD.org
user.name=Graham Perrin
%

There's a merge conflict aspect to 
<https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally>, 
however instructions there seem to be non-applicable.

Also, merge conflicts are mentioned in the Committer's Guide, but 
(sorry) I'm not yet at a point where I can put this in context.