Follow the below mentioned steps to merge the two .po files in order to prevent your previous translations:
(1) All you have to do is please download the provided .Po file from the ticket and extract it in a path say ‘Desktop’.
(2) Open your site’s existing .po file located in path ‘\wp-content\themes\Directory\languages\‘ or ‘\wp-content\themes\childtheme\languages\‘.
(3) Click on Catalog tab on top left corner.
(4) Press ‘Update from POT file’.
(5) In the pop up window, browse the new .po file placed on Desktop.
(6) Save the changes.
The above steps will help you protect your site’s existing translations and also helps to add the additional missing strings.
After following the above steps, all the required strings will be translated from .po file of Directory Folder only.
All the best! 🙂