Hi,
Shopify have recently released the ability to select metafields to edit with the product bulk editor.
It is on limited release currently - https://help.shopify.com/en/manual/metafields/bulk-edit-product-metafields
Might be worth checking if you can do that. Go into bulk edit and if you have access you will see your metafields in the ‘columns’.
Note: there is a fairly annoying fault with it though.
It is possible to spend a very long time editing only to then get this error when you hit save
The error message doesn’t tell you where the fault it so there is literally no way of correcting it. As I’ve just found out.
So…it seems like functionality is coming without using an app, but for now an app may be best until Shopify can make it usable.
If anyone from Shopify reads this - take this as feedback.