How do I fix this?

[MadMan]

Doesn't look that bad. The trim seems to have just swelled a bit and separated. Try squeezing it back together with glue under it, maybe use some big c-clamps for woodworking.

[EdKozk2]

If you want to re-glue the corner joints you could raise the set off the ground. If possible support the TV in the air on some plastic milk crates under the cabinet. The idea is to take the load off the skirting and sides. Then you can use clamps to hold the skirting in place after it has been re-glued. Place wood spacers between the clamp surfaces to keep the cabinet from being damaged. They make corner clamps if you need them, otherwise regular C-clamps should work. I use milk crates to support TVs when I want to remove threaded legs on consoles.
Ed