For edit multiple lines, click CTRL+V for init block selection. Click J or K for select the lines, or use arrows up/down.

Now with lines selected, press SHIFT+I for insert on all lines, or SHIFT+A for insert on the end of all lines.

ref: https://vimtricks.com/p/edit-multiple-lines-at-once-in-vim/

For basic find-and-replace on vim, we can use the :substitute (:s) command.

The general form of the substitute command is as follow:

:[range]s/{pattern}/{string}/[flags] [count]

The command search each line in [range] for a {pattern}, and replaces it with a {string}.
[count] is a positive integer that multiplies the command.

If no [range] and [count] are given, only the pattern found in the current line is replaced.
The current line is the line where the cursor is placed.

For example, to search for the first occurrences of the string "foo" in the current line, and replace it with "bar", you should use:

:s/foo/bar

To replace all occurrences of the search pattern in the current line, add the g flag:

:s/foo/bar/g

If you want to search and replace the pattern in the intire file, use the percentage character % as a range.
This caracter indicates a range from the first to the last line of the file:

:%s/foo/bar/g

We can also use | as parameter separator:

:s|foo|bar

To show confirmation for each substituition, use c flag:

:s/foo/bar/gc

To ignore case sensitivity, use i flag:

:s/foo/bar/gi

There is much more options, look at the ref link for more...

ref: https://linuxize.com/post/vim-find-replace/