Need a video of what
your quad does when
you try to fly it. At this point, it sounds like you have your PIDs reduced. You should go back to default PIDs and generally default settings. Make sure that Stabilization->ZeroTheIntegral... is ENABLED. Fly in Attitude mode (Stabilized 1) in your Flight Mode Switch Settings.
Does it flip over as soon as you give throttle? Does it jump up without flipping over and go way too high with less than 25% power? Are you talking about 3mm above hover power or 3mm above zero throttle?
When hovering, 3mm above or below hover power is actually a fairly large change and it will make it climb or descend quickly. When driving a car and following slowly 3mm of accelerator pedal will make a big difference in the distance to the car in front. The first thing to learn is to control altitude with the smallest motions possible like +- 1mm on the throttle stick. Many people use the "pinch the stick between two fingers" method because the "thumb on top" method does not easily give small, precise motions.
You generally
don't want to adjust the PIDs if it is simply too sensitive. There is are several other adjustments for that, depending on other factors. I don't think I have every heard the defaults for Attitude mode described as too sensitive.
You don't change the shock absorbers in a car if the steering is too sensitive. You change the steering gear ratio.
I believe that your problem is not one that should be fixed by changing PIDs, at least not yet.
One thing that often gets beginners is that we assume that you are running at least an ESC protocol that is at least as fast as PWM@490Hz or PWMSync. You will have problems similar to what you describe if you are running the ancient PWM@50Hz on one or more ESC. Make sure all your ESCs are running at least PWM@490Hz. Look in Output page and make sure all your Bank: and Mode: settings are the same and are PWM 490 or PWMSync.
Then there is ESC calibration. Do this to fix ESC protocol and do ESC calibration too.
https://librepilot.atlassian.net/wiki/spaces/LPDOC/pages/12058743/ESC+CalibrationIf you attach your settings file (File->ExportUAV...) it might help. Make a video of it trying to fly and link it here.