To update existing details of a variant you have to redirect to “Edit Variant” Page where all variant details will become editable. To edit variant details, follow path as follows
Business Profile > Operations > Manage Inventory > Select Product > Edit Variant
The product details will be opened and you can click on “Edit Variant” to edit variants
You will be redirected to Edit variant screen
Modify the details of the variants you wish to change and click on the “Save” button to update the modified details