Changing AllowOverride in .htaccess

Didn’t get much help on my original post:
https://www.ads-software.com/support/topic/40240
(thanks Class for what you could provide)…

So I thought I’d retry with a different subject line… I’m getting 404 errors on permalinks and I think the problem is that AllowOverride is not enabled. My host won’t enable it in the httpd.config file as suggested in the Codex (https://codex.www.ads-software.com/using_permalinks), and they say I should be able to change it in .htaccess. However, they won’t tell me how! I’ve tried adding

<Directory />
Options FollowSymLinks
AllowOverride All
</Directory>

to the .htaccess file, but it brings down the site with a 500 Internal Server Error. What is the proper way to do this? Thanks!