Sometimes we have to get a little creative to fix an "oops." The problem we need to correct may have been "self inflicted," such as when we pick up a clipper that we think has a comb attachment on it, and take a swipe of coat to the skin because really it's just a #30 blade. Other times we are correcting a haircut done by someone else. That someone might be the pets owner, a veterinary technician that got a little clipper-happy when preparing for surgery, or another groomer whose artistry differs from our own.
I encountered this grooming on the tail of an ancient miniature poodle last week. I see tails like this quite often, and you might, too. We call them "palm tree" tails. They happen when a groomer makes the tail band, much, MUCH too long, leaving a silly little fluff of hair on the end of the tail. It's not a good look, and there is really no way to completely fix it, because a lot of growing needs to happen before the tail pom can look the way it should. In this case, not only was the band too wide, I think they forgot to scissor the hair they did leave.
I find in cases like this, the best results come by taking the hair shorter all over, and blending as best as I can with scissors, chunkers, or thinners to try to make the best of a bad situation. In this case, I will only groom this dog one time while they vacation near me, then he will go back to the groomer that created this tail in the first place, so there was not a lot of sense in me trying to put a proper tail band on and work on growing a pom. So I trimmed the band area of the tail the same length as the body coat, and left just a suggestion of a pom on the end. This will leave the next groomer a little something to work with, and for the time being looks halfway decent.
Some "oops," can't really be fixed, and we have to be patient until enough hair grows to fill it in, but getting creative with shorter styles and blending can mask the area until enough time passes that we can really make things right.