Wyze thermostat installed but no air is blowing

My son installed the Thermostat last night. The only way we could get it to work was to put the G wire into the C spot and then go into the attic and put that G wire onto the C spot. Now it turns on. Both heat and A/C. But there is no fan blowing air from the ducts. Can someone help me? This is the video we watched. How To Install Wyze Thermostat Without A Common Wire (C Wire) - YouTube.

Also, there is a blue wire at the thermostat that is not hooked to anything. It is not stripped. Is this the wire that Should actually go into the C spot?

I hope this makes sense. I really have no idea what I’m doing so any advise would be well received.

G Terminal, its usually green wire, it’s for the indoor fan “trigger”, without it fan won’t run.
Blue (usually) will be connected to C terminal. You need to check there is a wire connected at C (common) terminal at furnace and that will be one going to C terminal at thermostat. There’s some guidelines for wiring color, but they not always followed. Check on furnace what colors are where, and repeat on thermostat side.
Older homes usually lack required number of wires. When G terminal gets connected to C trick, its a band aid fix for lack of a C wire. There could be some issues resulting from it and will not work with all furnaces. Fan circuit will be powering the thermostat, something was never meant too. I would look into getting a C wire transformer if possible, or a C wire adapter box.
How many wires do you have at thermostat?

There are 5. White, red, yellow, green and blue. But the blue was not being used on the old thermostat. The blue wire is just wrapped around the other wires and shoved in the wall.

That’s good. So, blue wire needs to be connected to C terminal on thermostat. Also needs to be connected to C or common furnace side.
Green to G (Indoor fan), Yellow to Y (cooling A/C), white to W (heating) and red to RC.
Make sure all those colors match at furnace terminals. This all assuming 1 stage heat, 1 stage cooling.

here are 2 blue wires at the furnace. Which one do I use for c?

Can u post a picture of the wires at thermostat? And another picture from slightly further out?
Definitely not the thick blue ones.

That’s a messy setup. I’m assuming the thicker brown cable goes to thermostat, and the smaller (one to the right of picture) goes to outdoor A/C unit, correct?
post pics so can better understand.