Maybe you sometimes find that VoiceOver speaks too fast for you to absorb information or maybe sometimes you'd like to speed it up to get things done more quickly. Fortunately there are several ways to change VoiceOver's speech speed. One method can even change the speed automatically when you use a particular app or type of app.
If you don't need to change the speed of VoiceOver's speech frequently go to Settings / Accessibility / VoiceOver / Speaking Rate and change the value of the slider by swiping up to increase speed or down to decreas speed in large increments. If you want to fine tune the value after you've set it to the nearest available value double tap and leave your finger resting on the screen until you hear rising tones and then slide your finger slowly left or right until you reach the desired value. You will only hear the effect of your chosen value when you've lifted your finger so it may take several attempts to get it just the way you want. You may also need several attempts before the double tap and hold gesture works as it should with the current value spoken as you slide your finger.
If you'd like to be able to change VoiceOver's speaking rate frequently depending on the task you are performing then it may be more convenient to use the rotor. Ensure that Speaking Rate is selected on your rotor and then when you need to change speaking rate, turn the rotor to speaking rate and swipe up or down to change the value in large increments. There is no fine tuning option. This will only save time if there aren't too many items on your rotor or you've moved Speaking Rate near the top of your rotor selectiongs. After you use the rotor to change VoiceOver's speaking rate I suggest you turn the rotor away from the Speaking Rate position to avoid unintentional speaking rate changes.
Another alternative is VoiceOver Quick Settings. To set this up go to Settings/ Accessibility / VoiceOver / Quick Settings and ensure that Speaking Rate is selected and either move it up the list by swiping up until it is at the top or near the top of the selected quick actions or maybe deselect any quick actions that are currently selected that you don't want to use. Once you've sset up your Quick Settings, you can summon the Quick Settings menu at any time with a quadruple tap with two fingers and then either swipe right to reach speaking rate or explore the screen by sliding a finger down from the top to find it. Double tap and then swipe up or down to change speaking rate.
Another option is to use VoiceOver Activities. An Activity can set a whole group of VoiceOver settings including the voice, its speed, volume and even its verbosity settings and then apply these settings using the Activities position on the rotor or set them to be automatically applied to specific apps or to contexts such as word processing or social media. You'll find the details in the Activities section of VoiceOver settings. This approach could be your best choice if you find you need to change VoiceOver's speaking rate when you use specific apps since that can be automated using Activities.