You can manage variant stock using the bulk edit option in the Variants module.
Open the product you want to update.
Click the "Variants" module tab.
Select the checkboxes next to the variants you want to update.
Click the "Edit" button.
In the "Setting to update" dropdown, select "Stock".
Choose "Custom stock".
Enter the stock quantity, for example
250.Optional: Enter a value in "Notify at stock threshold", for example
50.Click "Save".
The stock settings are applied to all selected variants.