You can mark the region to be quoted using
C-SPC if in Text mode and use
M-; which is bound to
comment-dwim and that will prompt you for a "Comment syntax" which you can then enter
> in the prompt.
comment-dwim to prefix the lines, you may also find
M-q which is bound to
fill-paragraph useful for wrapping the lines of the block quote if you're not interested in preserving the original line length.
Alternatively, if you have
markdown-mode installed, you can use
M-x markdown-mode to switch to it, and then mark the region you care to quote and use
C-c C-s q which is bound to
Finally, if you really want to use
query-replace-regexp from a terminal which I've found sometimes fails to work due to the combination of Ctrl, Meta, and Shift keys all requiring to be pushed at the same time, you may find it works using the following sequence
Esc key is essentially a "meta lock" key which will hold down meta for the duration of the next key sequence.