I am using Shreddit on Linux. It goes through each line in comments.csv from the GDPR export I requested, which is more complete than the data PowerDeleteSuite gets access to. PowerDeleteSuite basically clicks through your comment history on old.reddit.com and submits edit requests, while Shreddit uses the powerful API (it's not paid for personal use but you need to register the client, see the github page) and will find all comments thanks to the legally-mandated completeness of the GDPR export (if supplied; it will use the API to retrieve the comment list otherwise). BTW, you can alter the comments.csv for a custom filter (for example, I want to use a Czech string in Czech subreddits). You can use it on Windows (and it's an easier installation) but because of non-POSIX shenanigans, newlines in the replacement string won't work there.

If using PowerDeleteSuite, make sure to download the log file it supplies before you close the window or your original comment content will be lost!

If you're talking about your past reddit comments, I used this in the past: https://github.com/j0be/PowerDeleteSuite, not sure if it still works though.