StackOverflow isn't a code request service, you're supposed to provide the code you need help with!
Here's an idea to get you started, it simply replaces the everything up to and including :
@Echo Off
For /F "Tokens=1-2 Delims=:" %%A In ('FindStr /INC:"" *.html 2^>Nul'
) Do (( Echo ^
Echo ^
Echo ^
Echo ^
More +%%B "%%A")>%%A.mod)
Your modified files will have the extension .mod so you can check them out
Edit
This example, doesn't close the
tag!@Echo Off
For /F "Tokens=1-2 Delims=:" %%A In ('FindStr /INC:"
" *.html 2^>Nul') Do (( Echo ^>
Echo ^
Echo ^
Echo ^
More +%%B "%%A")>%%A.mod)