indent-rigidly (C-x TAB or C-x C-i, see footnote) can help you.
indent-rigidly is an interactive compiled Lisp function in
It is bound to C-x TAB.
(indent-rigidly START END ARG &optional INTERACTIVE)
Indent all lines starting in the region. If called interactively with
no prefix argument, activate a transient mode in which the indentation
can be adjusted interactively by typing left, right, S-left, or
S-right. Typing any other key deactivates the transient mode.
If called from a program, or interactively with prefix ARG, indent all
lines starting in the region forward by ARG columns. If called from a
program, START and END specify the beginning and end of the text to
act on, in place of the region.
Negative values of ARG indent backward, so you can remove all
indentation by specifying a large negative ARG.
Footnote: C-x TAB is equivalent to C-x C-i. This was noted by nanny in the comment, and I think it's worth mentioning because C-x C-i is so much easier to hit.