How to bulk edit product variations in WooCommerce

To bulk edit product variations in WooCommerce, switch the Products Editor into variations mode and then use either binded editing or the Bulk Edit tab:

In the Filters tab set product type to variable and press Filter, so only variable products are on the pages.
On the tools panel lower Per page to about 10: every product now brings its variations with it, and a page of ten variable products can be a hundred rows.
Switch on variations on the tools panel. Every variation appears as its own row, and from this moment bulk and binded operations touch the variations only; the parent products are ignored.
For a handful of variations on one page: tick them (the select all variations button ticks the whole page), switch on binded editing, and type the value into any one of them. The same value goes to all ticked variations.
For all filtered products: open the Bulk Edit tab. With the variations switch on, the form hides the fields that variations do not have and shows a block where you name the attribute combinations to work on, for example blue + large and red + small. Variations that do not match are skipped; leave an attribute unselected if it should not take part. Then set the field, the behaviour and run.

Price, sale price, stock quantity, stock status, SKU and weight are the usual fields here; each behaves as it does for simple products. Every run lands in History and can be reverted. The video chapter shows the same steps on screen:

Documentation for BEAR - WooCommerce Bulk Editor and Products Manager Professional: tabs, tools and developer guides