The command should be in one line with no breaks.
It's a combination of two commands: the grep lists all the files that match the pattern (regular expression) and hands them over to the sed, that does the find & replace part. If the grep doesn't find any files, it won't work. The pattern I used is: 1. a colon ( 2. a plus-sign (+) 3. either 8 or 9 4. seven digits (from 0 to 9) 5. end of line ($)
Maybe you find a pattern that works or you give me an anonymised vcf-file for testing purposes.