remove from tag

Hi! Can you help me with simple tag renaming please:
How can I tag title from "Some Name#something" transform to "Some Name" ?
I think I should use Actions - replace with regular exp, but my expressions like $1#$2 doesn't work

If the # separates the 2 bits of data then use an action of the type "Guess values" (import tag)
Source: %title%
Target: %title%#%dummy%

For the replace action you would need
Search string: (.)#.
Replace string: $1