Hi,
TortoiseGit does not allow to rebase the root commit with the
rebase dialog right now (cf.
https://tortoisegit.org/issue/3018).
However, you could do a workaround, e.g. create a new branch on the root
commit, switch to it, change and amend it. Then rebase the old branch
onto this new commit (or reset to the root commit, change it, amend id
and then cherry-pick all newer commits or rebase the pother branch onto
this commit).
Or use git cli.
--
Best regards,
Sven Strickroth
PGP key id F5A9D4C4 @ any key-server