Help me to resolve this error in this LTSpice Simulation
You have no model for the opamp, every component needs a model:
add the line .lib opamp.sub for further reading on adding models see these links
https://www.analog.com/en/technical-articles/ltspice-using-an-intrinsic-symbol-for-a-third-party-model.html
How do I import a spice model into LT spice?