Silly question about a KSA 250-Fuse


Sorry for the silly question but does anyone have any advice on how to change the rear ac fuse? Can't seem to turn it. Theres a round, ribbed inset that looks like it should turn but isn't. Thank you in advance. 
duran
From the user manual..............................................................................

  G. WARRANTY AND SERVICE INFORMATION There are no fuses or user-serviceable parts in the KSA-150 or KSA-250. Both amplifiers have a limited warranty of five years from the date of purchase for parts and labor.
@ duran


Is this a picture of the back of the amp?
https://www.ebay.com/itm/192768389378

If so that is not a fuse holder. It is a 20 amp circuit breaker. If it trips you push in on it to reset it.

.