How to change language after .po file upload

Hello,

how can i change the language of the plug-in?

I already downloaded the german translation from this website https://translate.yithemes.com/gp/projects/yith-woocommerce-gift-cards/de/default/?filters%5Btranslated%5D=yes&filters%5Bstatus%5D=current and uploaded the german .po file in the language folder of the plugin.

However I do not know how to activate the german language now.

Kind reagrds