Hi Nibal,

I know that learning anything new can be frustrating and take a while, but you show real initiative. It sounds like you're learning AutoCAD AND LandFX (AutoFX and IrrigationFX) all at once with little mentoring or training. I take my hat off to you, but you may want to change your approach a little.

The way that we control line widths of any AutoCAD entities is with layers. Different layers, set to specific colors, plot different widths depending on the pen width that we've set in the plotter configuration. That's why setting the layers for LandFX objects in the preferences is so important. This way our legend matches our plan. Beware that in AutoCAD "thickness" is more of a 3D term. You want to set the "Width". You can do this by changing the entity into a polyline and setting the width, but to set the printed width of lines you'll be setting that entity to a certain layer (such as IR-LATR) and then setting the color of that layer to print a the correct width in printer configuration.

Don't know if this helps. Good luck.

On another note, If you want to modify any of the irrigation blocks to beet your office design standards, here's a good place to start. But I'd start whit layers first. It's a lot easier.
https://www.landfx.com/index.php/docs/irrigation/customize-irrigation/irrigation-symbols.html