I created my own custom fields using ACF for dimensions (height, width, length).
In the WooCommerce shipping section these dimensions exist too (slugs: _height, _width, _length)
I want to enter these 3 dimensions in the ACF custom fields and I need these values to automatically populate the WooCommerce shipping dimensions and the other way round. In other words they always need to be mirrored.
You need to find the database names of the fields in woo. Then you need to create and acf/save_post filter https://www.advancedcustomfields.com/resources/acfsave_post/. When the post is saved with the ACF fields you need to get the values of those fields and use update_post_meta() to update the woo fields.
woo may have it’s own function to do the same.
The other site, you need to figure out what hook in woo to add a filter to in order to copy the values in the other direction. You’ll need to get this information from woo support.