Ok, first... let's establish which "under-awning" lights you have...
There's the type that simply adhere to the sidewall of the RV, right under the attachment point of the awning to the RV...
And then there's the type that adhere to the awning roller-tube, fitted into the '4th slot'.
If it's the first type, they are simple to purchase (available many places, including Camping World), and usually pretty simple to install... requiring only an appropriate power source to tap into.
The 2nd type is a little more complex. You can buy the kit from Carefree... but the trick is how it's wired. Here's a link to the kit:
LED Lights - Carefree of Colorado
The main issue is convenience, in re how to get power to something that rolls up on a tube.
If you have the 2nd type on your main awning... you'll notice that the edge seam near the front door is a tad thicker than the seam on the rear. That's because the power-wire is pre-sewn into the awning... it connects to the LED light ribbon easily at the roller, and rolls itself up along with the awning when retracted.
If you buy the kit above... well, obviously the power-wire isn't sewn in. That means you'll have to plug & unplug it everytime you extend/retract the awning... or either try to sew it into the awning yourself.
Anyway, those are your options... but, yes, it can be done.