Terraform’s “autocomplete” support is implemented in terms of a third-party library, which is where this error message originates. From looking at the source code of that library I see that its strategy is to search for a number of possible shell configuration files to add its configuration to:
It seems that the error you saw results from this function not finding any of the files it is searching for. Since you said you are using bash I think the series of bash configuration files are the most relevant for you:
You should then have an empty file .bashrc in your home directory. If you then run terraform -install-autocomplete again, it should hopefully find that file and append the Terraform autocomplete setup code to it, and then after you restart the shell it should take effect.
On Unix systems an initial .bashrc (or similar) file is typically created when adding a new user to the system, so I think the autocomplete library is surprised to encounter a situation where you have no configuration file at all.