01title to 01.title

As said in title, I have filenames that are TrackTitle, I would like to change to Track.Title.
I have tried this method but without success, please tell me how I can do it.
I have tried doing:
Action:Replace with regular expression
Regular Expression:^\d{0,2}
Replace matches with:$1.

You need parentheses to make $1 work:

Regular Expression:^(\d{1,2})
Replace matches with:$1.

ah thank you!