Servos

It needs the safety on (model disarmed) and a Version 2 receiver with Bluetooth. With no model, the page shows the model's backup on the card, if one was made: a 'Save' then changes the backup, and the change is offered to the model when it next connects.

Tap a number to type a new one.
Tap a switch to change it (green = on).
'< Servo' and 'Servo >' step through the servos. The title says which one you are on (Servo 2 of 4). Servos 1, 2 and 3 are usually the swashplate, 4 the tail.
'Save' appears once something is changed. It writes this servo to the flight controller, stores it there and reads it back.
Save each servo before you move on: a change not saved is dropped (it asks first).
'OK' leaves; if a change was not saved, it asks first.

The settings

Centre [us]: where the arm sits with the sticks centred, in microseconds (750 to 2250). Adjust it so the linkages are level.
Min and Max [us]: the stops. The servo never moves further from the centre than these (-1000 to 0, and 0 to 1000).
Scale neg and Scale pos [us]: how much arm movement a full stick asks for, each way (50 to 1000). Usually both the same.
Rate [Hz]: how often the servo is sent a new position (25 to 5000). Never more than the servo's specification allows.
Speed [ms]: slows the servo down. It is the time the arm takes to move 60 degrees (0 to 60000). 0 = full speed (normal).
Reverse: turns this servo the other way, like a servo-reverse switch. To reverse a control (aileron, elevator, collective or yaw), use 'Mixer ...' on the Rotorflight options page instead.
Geometry correction: evens out the arc of the servo arm, so equal commands give equal swash movement up and down.
Usually on for the three swashplate servos.