Connecting Sub Ground to Main

A year and half ago I set up my sub panel around the back side of my home for pool equipment and further outlets and patio lighting/fans.

I set 3x #3 copper THHN in a 1.25 ENT in the ground from my main panel (new ’08) approx 170 feet around the back of my home to the other side of my home for a new QO load center run by a 2 pole 80 amp breaker in my 200 amp panel.

I didn’t find that I needed to run the ground from the sub to the service main,only that the sub needs its own ground and the bond screw in the sub is removed.

Now I’m seeing that I do NOT meet code by not having the sub ground connected to the service main.

What would be the best way to upgrade this oversight?

Can I connect and bury a ground wire (#4 copper) to my ground rod for my sub and run it in the ground, not in a conduit, around to the ground rod for service main? I know where the rod is located.

Or must I run that ground into the main service panel to connect to the ground bar in the main panel?

---

I did not use ENT, I used rigid PVC electrical conduit and fittings glued together buried 18 in down all the way around my house through the walls and into the service panel. I was thinking about ENT while typing and didn’t catch that I used an 80 amp Eaton breaker in my 200 amp main service panel. The QO load center I put in is rated to 200 amp but I didn’t need that much, but I intended on over sizing the feeder wire to be good on wire size. I don’t need 100 amps on that sub right now so 80 should be fine. The 1.25 pipe has a number of turns in it so I can see challenges getting through it, and the 3 wires may be twisted at some point.

QUESTION: Would I need to pull out all three wires while pulling in a pull cord, then reset to pull the three and the ground after that?