Find all files in the current directory (maxdepth 1), and for each file, execute a sed command to replace any string of one or more digits followed by one or more spaces followed by one or more alphanumeric characters or underscores with the alphanumeric characters followed by the digits.
find . -maxdepth 1 -type f -exec sed -i 's/\([0-9]\+\) \+\([a-zA-Z0-9_]\+\)/\2 \1/g' {} \;