How to insert link from text to another part of the document.
You probably mean a cross-reference. Word link is rather used for “links” to web pages or other documents.
Always mention OS name, exact LO version and save format.
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→ How do I jump from one part of LibreOffice Writer document to another?
First use >Insert>Bookmark... to create a bookmark on the target position or (single) textrange.
Now you can use the Navigator to easily jump to that bookmark from anywhere.
If you definitely want a link from a specific text portion you can select this “elsewhere” and use the tool Insert>Hyperlink...>>Target in document, then select from the icon right of the line Bookmarks and finally the one you want.
The link you created this way will also be shown in the navigator.