VoiceOver provides all of the usual text editing tools for selecting text and then deleting, replacing, cutting, copying or in some apps, formatting the selected text. If Cut or Copy are used on selected text then that text may be pasted elsewhere into the current document or into text in any app that edits tex, including Mail and Messages. If you have used a computer then you will probably be familiar with these tools already but I will outline them briefly below. The full set of tools is available only when text is being edited. However, you will be able to use most of these tools in many apps when you aren't able to edit text with a double tap, such as copying a section of text from an email you have received into a document of your own.
Before you begin, please ensure that the Text Selection tool is enabled on your rotor. You may need to place this on your rotor in Settings/Accessibility/VoiceOver/Rotor/Rotor Items.
Ensure that you are editing the text and that a keyboard is present at the bottom of the screen and then move the insertion point to just before the text you want to edit. This will normally be done using the characters, word or lines positions on the rotor just as in simple text editing.
Turn the rotor to text selection. VoiceOver will speak "swipe right to expand selection; swipe left to shrink selection". Unfortunately VoiceOver's hint doesn't also mention that you first need to perform another action. The text selection tool is a little unusual and before you start selecting text you must tell the text selection tool how much text you want to add to your selection with each swipe right and remove from your selection with each swipe left. This is done by swiping up or down with one finger which cycles through the available choices of select all, page selection, line selection, word selection and character selection. Your choice will be determined by the size of the section of text you wish to select. If the section ranges over several lines, then line selection will probably be your initial choice but if you don't want to include all of the final line in your selection, you could change to word selection when you reach the final line in order to add the last few words to the selection with your last few swipes to the right. If you overshoot, text may be removed from the selection with a swipe left. Every time you swipe right or left, VoiceOver will speak the text that has been added or removed from the selection. If you don't want to hear this in full, you can continue with your next swipe right or left as soon as you wish or you can tap with two fingers to pause VoiceOver's speech. If you want to check the selection at any stage in the process, tap with three fingers and VoiceOver will speak the whole selection.
The simplest action is to delete or replace the text by tapping the delete key on the keyboard or by entering replacement text on the keyboard, by dictation or any other text input method. If you want to move the text to a new position in your document this is done by turnin the rotor to Edit and then swiping up or down until you hear Cut. Double tap to perform the Cut which will remove the text from its current position and place the text on the clipboard. Position the insertion point to the new location for the text, ensure the rotor is on Edit and then swipe up or down until you hear Paste. Double tap and the text will be inserted at its new position. If you wanted to leave the text where it was and insert it into another document use Copy instead of Cut and the text will remain in its original location but a copy of it will be on the clipboard and can be pasted into text in any app that edits text, for example Mail or Messages. Some apps, for example Notes, offer additional formatting options on the Edit rotor as you swipe up or down.These may include items such as set italic or set bold. Word processors such as Pages may have more sophisticated formatting tools in their toolbars which offer full control over the appearance of your selected text. Depending on the app you are using, other actions may be performed on selected text I'll leave you to discover these in those apps.