It is a temporary power, and should be in your power tray to use like any other power. Just target a valid RIP member, get in range, and then use it.
Let me never fall into the vulgar mistake of dreaming that I am persecuted whenever I am contradicted.
~Ralph Waldo Emerson
"I was just the one with the most unsolicited sombrero." - Traegus
And if it's not in one of your trays on the screen (which can happen if you've filled up all the slots on all three of your first three power trays), open your Powers screen and hunt through the temp power list for it.
This sounds like a low level mission so his trays shouldn't be filled up. However, since the OP sounds like a newbie, perhaps he still only has powers tray #1 opened and it is filled with assorted powers.
FrogDave, have you expanded your powers trays to show tray #2 and #3? If not, on your powers tray's header bar, on the far right, there's a little up arrow. See example (note: mine is a down arrow because I've already expanded to 3 trays). Click it twice to expand your trays. Three trays might look like overkill right now as a lowbie, but you'll be filling them out later especially if you have permanent "temp" powers you like to use.
Note: if you find that your trays are getting cluttered with power buttons that you never use, you can right-click them to remove from your tray. Don't worry if you're not sure if you may want it later. All your powers, including temporary ones, are listed in your Powers window (click the "Powers" link on your powers header bar to open it). You can drag and drop powers from Powers window back to your Trays anytime you want.
Note: if and when you find that 3 trays aren't enough for you, you can click that little plus sign (+) next to the arrow to open additional free floating single bar trays. You can right-click on these floating trays to make them into rectangle shapes or you can shove it against the left or right side of your screen and they'll deform into L-shapes. Of course, you can right-click them to remove the tray if you don't need them anymore.
Teams are the number one killer of soloists.
I just started playing a villain, and I recieved a quest to use a syringe on some RIP. How do I use the syringe?