Hello Sabine,
You are following good instructions but may need a bit of tweaking.
This forum is a user-to-user support forum. My name is Charles and I am a fellow user with decades of experience using Microsoft Word. I have written extensively on using Word and have authored help articles on the Microsoft site.
There is both a right-tab and a right-indent there. You need to move the right-indent without moving the right-tab. Probably the best way to do this is to use the paragraph formatting dialog rather than the Ruler.
The formatting is contained in the various TOC styles, TOC 1-9. By default, these styles automatically update so that when you change one entry, it changes the formatting for all entries of the same level.
I hope this information helps.
Please let me know if you have any more questions or require further help.
You can ask for more help by replying to this post (Reply button below).
Stay well