You are basically doing a reverse CRO. I recommend adjusting stock down, and adding again every morning. Raise shipping costs. Do not run any offers. And communicate to the customer, that due to Covid19 fulfilment can take a lot longer, and then they should hire in more people to fulfil orders. Once the situation is under control, then you should reverse all the actions, but I would wait with the ones that are an actual cost, such as the freight. That way they have an excellent way of making the business more healthy.