This is not a typical CAD feature and there is no 'curved text' tool in LibreCAD.
You can do it step by step, letter by letter.
Or you can use DTP software like inkscape. Curved text shouldn't be a problem in inkscape and you can export to DXF format.
But, I haven't tried that yet, no practical experience.
Armin
investing less than half an hour into Search function can save hours or days of waiting for a solution