This snippet is one of several ways to find and replace words or strings in multiple files.

grep -rl 'Fickel Fritze' . | xargs sed -i '' 's/Fickel Fritze/Frickel Fritze/g'

Here grep returns the filenames of files in the current directory and recursively below. Flag -r results in recursively visiting files starting at the current directory. The -l flag causes grep to output only filenames instead of the matched line.

xargs reads input from stdin, which here is piped from grep, and iteratively applied to a command to the right of xargs. In the current example, the filenames are applied to sed.

Sed is run with the flag -i (in-place edit). While in most sed versions, the -i flag takes an optional parameter of a file extenstion to make file backups before in-place modificiation, this entry is mandatory on all to me known OSX versions (here currently 10.14.1 / Mojave). If no backups are desired, an empty string '' has to be provided for the syntax to be correct.