I need to merge Avery labels with data from another file
Unfortunately your question is missing information. Please take a moment to review the following.
On the main page after you sign in, there, in the right hand column, is a section called
Resources. Please read How to use the Ask site. It’s not all encompassing but will provide basic information to ask a bit better question. Also of help is this post → Guidelines for asking
If you are just looking to print labels, see this documentation-> LibreOffice Writer Guide, Chapter 14 - Mail Merge.