One way would be to download a PNG circle image via an image search and place it on track 2 (the overlay track).
Another approach...
Download a high-contrast circle.
Place your text on track one and the circle on track two.
Click on FX in the circle clip on the timeline. When the effects editor opens click the large green + at the top-left and choose GREEN SCREEN.
Use your mouse to maneuver the color picker in the preview window to the background area. Click. The background should vanish. Adjust the sliders for best presentation.
Using either method, employ the SCALE, POSITION or other effects as needed.
