It looks necrotic... I'm very sorry to be the one to say it but you need to end his suffering in the quickest and most humane way possible. I'm so sorry

EDIT: I took another look and it appears he is prolapsing around a large fecal mass?? Either way this frog needs immediate vet help, if this isn't possible then I stand by my original statement. This sounds awfully harsh, even to me, but I'm speaking from very painful and raw recent experience (frog with multiple prolapses who had to be put down)... your frog is suffering and you don't want to prolong it.