for var in value do echo "$var" done
Correct code depends on what you want to do.
To iterate over files in a directory, instead of
for var in /my/dir use:
for var in /my/dir/* ; do echo "$var"; done
To iterate over lines in a file or command output, use a while read loop instead:
mycommand | while IFS= read -r line; do echo "$line"; done
To iterate over words written to a command or function's stdout, instead of
for var in myfunction, use
for var in $(myfunction); do echo "$var"; done
To iterate over words in a variable, instead of
for var in myvariable, use
for var in $myvariable; do echo "$var"; done
ShellCheck has detected that your for loop iterates over a single, constant value. This is most likely a bug in your code, caused by you not expanding the value in the way you want.
You should make sure that whatever you loop over will expand into multiple words.
ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.