replace nav double arrow "?" with single "

I’ve looked high and low and can’t find the file where I can replace the double arrowsrel="next">?</a> with a single. Code appears when I Inspect Element in Chrome but a search via ftp files on the server both .js, css, php, came up short.

Would really appreciate if someone can point me in the right direction. thanks!

https://www.ads-software.com/plugins/wp-single-post-navigation/