Wear a glove...take it out in the night when yr zoas and surrounding corals are "sleeping"...dig yr hands into the sand bed and scoop it up from the bottom.
Before you do all that, remove some of the surrounding corals next to it and place them away temporary.
Btw, where are you gonna house yr anemone? Intend to place it into a pail ? (put a piece of rock inside the pail and with an air pump to provide oxygen)
(planting it in chek jawa? haha)
Do it slowly you dun wanna cause too much stress to your fishes...all the best!
FYI, i used to buy an yellow anemone out of impulse also...tot it wd be nice to include it into my tank...haha
You may want to include one or 2 live rocks behind yr tank...so you place some of your corals on top. Your tank will have some depth to it, not so flat...