Ballnut install Seig X3 cnc conversion

I am having a hard time figuring out how to install the nuts into the ballscrew in the pic. Any advice?

Ideally the nuts would not be separated from the screw. If the nuts came separate from the screw then they probably had cardboard tubes in them holding the balls in place. You would have carefully inserted the screw into the nuts keeping the balls in place while simultaneously withdrawing the tube.

Look up YouTube videos on reloading ballnuts.

If you have two assemblies...that are disassembled, keep track of which screw goes with wich nut and set of balls. Sometimes the balls sizes are selected to go with the nut to reduce backlash.

And one more hint, when you do the re-assembly, don't have any coffee and prepare yourself for a test in patience.

You may well regret the situation you find yourself in, I speak from experience,

I always drink some bourbon when I repack them. It helps calm the nerves, the process definitely isn't one of my favorites, though I have gotten decent at it.

If you have to put the balls back in it helps to pack it with grease. The balls stick in place (mostly).
Where did the cardboard/plastic tube go or did you just take it off the screw yourself?