The .htaccess file is hidden. So the only way to create a redirect is to create your own .htaccess file on your PC and overwrite it by uploading it on the server. This answer was useful: https://answers.afrihost.com/33/how-do-i-create-a-htaccess-file
This is the process I basically went through in case anyone else has a problem:
1) Click on the htaccesseditor link suggested on https://answers.afrihost.com/33/how-do-i-create-a-htaccess-file.
2) Once your on the website click on 'Error Page (E)'. Type in the URL of where your 404 errors should redirect to.
3) Click on 'Default Page (D)'. Type in the filename + extension (eg. index.html).
4) Click on 'Setup WWW (W)'. Type in the URL of your website.
5) Create a file called '.htaccess' on your PC. Copy the content into your '.htaccess' file.
6) Upload the '.htaccess' to your 'public_html' folder. Click Yes if requested to overwrite.