does reordering (it is option in resolution center to reorder) will affect my gig? A buyer placed an order and now want to reduce price because of less work. Is it possible?
The ONLY way to reduce the price of an order is for you to make a new one, the Buyer FULLY completed the new order, then you cancel the original one. This is messy and will affect your completion rate.
will mutually cancellation also affect my gig?
Yes. You can try to connect with Fiverr Customer Support and ask that they cancel the order for you without affecting you (once the new order is FULLY complete), but it’s iffy if they will.