How to add additional theme strings to strings-translation setting (Interface)

Hi, I am using your plugin for 1 years now, and works great! Thanks!
Yesterday I changed my theme to Interface theme. And I would like to translate Slogan content in theme options. But I don’t know how. I can’t find it in Polylang’s language > settings > strings translation.
How can I add to this?

Thanks for your help!

Mantraagnes

https://ww.wp.xz.cn/plugins/polylang/