guys! I am trying to exchange two words in a line but it doesn't work.
For example:
"Today is my first day of university" should be "my is Today first day of university"

This is what I tried:

sed 's/\([a-zA-z0-9]\)\([a-zA-z0-9]\)\([a-zA-z0-9]\)/\3\2\1/' filename.txt

What am I doing wrong?