How do you change pull starter cord on honda es 3000 is generator?

from your description sounds like a seized motor remove plug and try to turn over motor

if its a generator No because the engine needs to be set at 3000 rpm constant or it will damage what ever its running

The pull cord is like a starter on a car (separate from the motor/engine). If the pull cord will not turn it could be because the motor/engine is seized.

check the battery?

What you need to do is first remove the new cord that you installed.
(This next process is best performed by 2 people)

Pre-wind the spool gently COUNTER CLOCKWISE until the spring prevents further winding. Have the 2nd person grip the spool so that it does ot unwind. Back off the spool until the re-wind rope hole is aligned with the outer cover rope guide. Insert the new rope through the outer cover rope guide hole and into the spool hole. Pull the new rope through the spool hole and tie a single small knot. Pull the knot into the hole. 2nd person releases the spool and the rope will rewind into the re-coil assy.

Try removing your spark plug, you could have fuel on top of the piston or even "vapor lock". If that doesnt work try squeezing the trigger of gun/wand as you pull.

pour some gas/oil mixture down sparkplug hole and let it soak and see if the rings are carbon blocked