Reply To: merging multiple lines into one TOC entry

What you’re describing there cannot be done with TOC feature.

You could do it with the Cross References

Have the Chapter Headers as paragraph names Chapter Heading Line 1, Chapter Heading Line 2

However, this is awkward to setup – and if your text changes it breaks the cross reference link.

I am not a cross reference expert so maybe there’s another better way.

See sample file
https://www.filedropper.com/untitled-4

You will need to open the Window>Types & Tables>CrossReferences