I turned my ryobi 6.5 over to replace the blade, afterward it started 1st pull, I stopped it to add oil and gas, now it won't fire, even when I prime it.

When you turned it over oil probably got into the piston cylinder. Pull plug, pull rope several time to blow out cylinders. Reinstall plug and start.

If there's oil residue on the plugs and cylinder it won't fire.