I'm not sure beads would fit inside the hole for the type of bridge the nova u has..Hello,
One cheap and efficient way to solve this issue once and for all is to put on string beads on each string before tying the knot. Plus, the beads apply a more even pressure on the soundboard and avoid any snapping.
Hope this helps, regards.
Cut the string shake out the knotted end through the sound hole slits.
Push the string in at the bridge until a few inches still remain hanging out. (You can tie the end off with a paperclip or other item so it won't pull through. Rotate uke so neck is towards ground. Shake the body a few times. Use a straightened paperclip with small hook bent into the end, or other thin item to fish the string out of the body through the sound hole slits. Cut or untie the other end and pull string out through the soundhole.
It will be a little fiddly, but be patient and go slowly. you'll get it out.
A pin or a needle would be better. It's too easy for an Xacto blade to damage a plastic slot. A pair of needle nosed tweezers would also work. Anything that you could use to push the string down out of the slot so you can work it back to the hole to extract the knot.Did this work? If not, maybe sticking a narrow, pointy exacto knife into the slot and carefully trying to move the knot around enough to free it.