@denatx
IF you can find that order in your database, then drop/delete the commission line for it.
GO to the pv_commission table in your database. If it is not an issue since this is a test vendor, then no worries. 😉
Yeah, in the future if you wish to delete an order, first mark the commissions REVERSED. Then it can be deleted without an issue.
wp admin > woocommerce > commissions