How to get rid of all tab stops in a text document

edit

First delete all tab stops in one paragraph:

1. Place the cursor in one paragraph.
2. Choose menu Format - Paragraph… - Tabs, press Delete All and OK.

Next, delete all tab stops in the other paragraphs:

1. Select (at least part of) all the paragraphs from which you want to remove the tab stops.
2. Choose menu Edit - Repeat: Apply atributes (same as Ctrl+Shift+Y).

Now, set the new tab stops:

1. Select (at least part of) all the paragraphs in which you want to set tab stops.
2. Choose menu Format - Paragraph… - Tabs, select Position and Type, press New and OK.

More LibreOffice Help on Tabs.

Also consider working with Styles. They can save you a lot of work.