You can Glue it on with gorilla glue or sticky silicon glue. The inner part of the bezel is called a bezel insert, I have looked all over the net for ways to repair it and have only found one video as listed by the poster above. But if you entirely lost your bezel insert on the street or anywhere and do not have one in possession, you can just get a bezel insert from a old watch or order one . After getting a new insert, you can just glue it on. Just be sure to find the right size, for example: if the bezel size is 44mm, buy a 44mm bezel insert. This will work.