how do I increase natural gas pressure on outdoor fireplace
If the pressure you're measuring is the static pressure, that is the pressure in the line with no gas flowing, that pressure is the same everywhere in the line. You cannot increase that pressure by removing unneeded gas pipe. Instead, you can try having the gas company adjust or replace your regulator.

If you're measuring the pressure while gas is flowing, you might have lines that are too small, long or bendy. You might also have a gas meter that's undersized or defective. I again suggest calling the gas company to see if the meter needs to be replaced.

It's really in everybody's best interest to just call a pro. But the gas company should be happy to at least answer your questions, since you're trying to use more gas. If the meter or regulator needs service or replacement, they should do that for free.