How to import parts of a tag name into a different tag ?

How to cut a leading part of the title tag (up to 1st space or character "/") and move it to the Composer tag ?

Example :
Title "Bach / Chaconne from Partita No.2" ...would be called "Chaconne from Partita No.2"
...and Composer field (empty) would show "Bach".

Take that as example
and adapt to your needs.

Thanks a lot !