It is enough to engage Rescue mode on the ground. Swashplate must go always Upwards, so that there will be clearly positive pitch between main blades. So if you will set 80% rescue collective pitch, it should be at 80% of configured total pitch range.
If this is not the case, then I am afraid the basic settings is wrong
For example servo wiring or channel reversing. But this can be easily verified all in the Diagnostic tab - aileron, elevator, rudder, pitch channels must correspond to actual stick movements, including direction there.