By using the IPriceDetailService:

https://world.episerver.com/documentation/developer-guides/commerce/pricing/Pricing-examples/

Here is a starting point https://vimvq1987.com/permanently-drop-prices-products/

You can change UpdatePrices to something like this

            var prices = _priceDetailService.List(contentLink);
            _priceDetailService.Delete(newPrices.Select(x => x.PriceValueId));

You can also use IPriceService.SetCatalogEntryPrices() which can delete prices if you pass an empty price list.

It'd be interesting to see which is faster ...