Nice aquascape, I like your rockwork. Looks nice.
I also think you should remove it and QT. Doesn't sound like you medicated already, and if you don't have meds, at least pull it and get a QT started with fresh made saltwater (aged, aerated 24 hours works best). Just looking at how white those rocks and sand are, and it's just my opinion (a guess), that anemone may struggle to adapt to that tank in the condition it's in. NOT that it's bad, but still may be a little on the "too clean"/new side... QT may help it acclimate to your tank/water better. At least start by getting it an internal "water change", then try using your tank water in QT, after it improves, to see how it reacts. Getting an anemone that's in "poor" shape to acclimate to a tank that's in "moderate" condition (not that your tank water is bad, but time helps establish ) may be a struggle. Getting an anemone in "good" condition will be easier to get acclimated to a "moderate" condition tank, if this makes sense. Your tank looks like it should be ready to support an anemone, but you need to start with a healthy one. This anemone is not healthy right now.
I would still order meds, but by the time they come, you may find it doesn't need meds if it starts looking better, it may just need to "change it's diapers"....

But keep in mind, the stage yours looks to be in, some don't make it from this point (some do), so sooner action is better. Best of luck to you.