@PriyanshuGM smooth(Throttle,x)
x can be whatever you want, the lower it is, the slower your acceleration. The only issue is that your throttle will be less responsive.

@ReinMcDeer how to use the smooth function then cus i need the power

@PriyanshuGM It does, but that'll slow the acceleration. You could also use a smooth function for the throttle input if you still want the full engine power, but it's up to you.

@ReinMcDeer doesnt that makes the engine weaker?

@PriyanshuGM Yep! Go into Overload and look for powerMultiplier and change it to whatever value you need. You'll probably need to reduce the drag of the airframe too to maintain your top speed.

@ReinMcDeer and do you know how to slow the acceleration of a jet engine?

@ReinMcDeer thank you so much for helping

@PriyanshuGM Unless it's really major, enabling manual trim is the best option.
If you're fine with redesigning your aircraft, the throttle input pitching your aircraft means that your center of mass and center of thrust are not aligned. You could try moving your engines up or down and see if that helps.

@ReinMcDeer do yk any other way,my plane pitches up to down depending on the throttle percentage

Although, the plane pitching one way by itself is actually normal and is why trim exists.
There are ways to fix it with FT using PitchRate, but they usually end up oscillating up and down instead of staying level.

@PriyanshuGM Hmm... Is the aircraft pitching up, or down?

@HuskyDynamics01 that changes with percentage of throttle so its just useless in this case

There's probably some complicated way to fix this with FT, but a much simpler solution would be to just move the center of mass forward or backward a bit, depending on whether the aircraft is pitching up or down.