lg monitor water have screen was switch off

@khaleelsha33873 we need to know what model your monitor is. Ultimately you need to treat it just like anything else that was exposed to water.

You need to disassemble it, clean all the board with a high grade isopropyl alcohol and expect your board for corrosion. Corrosion will be your biggest enemy. Keep in mind that water damage is the hardest to troubleshoot and to repair. It does not matter if is was exposed for 2 seconds or 2 hours, what matters is where the water (particulates) did the damage.

We can't be more specific since you did not leave specific details in your question. ¯\_(ツ)_/¯