How to replace ^M with normal line break in Vim

by pressing <control-v><control-m>, you can type in the vim command line ^M,

where <control-v> is to press v while pressing control key.

In vim command line, try

:%s/<control-v><control-m>/\r/g

or

:%s/<control-v><control-m>//g

(When I tried the first one, an extra line was added, which I didn't need.)