Then I continued with the old thread. I put it around the new thread from top to bottom to form the chain.
I made the knot like a normal cable chain stitch and took the needle to the back.
Then I pulled the old thread through, holding the new thread tight.
I stitched a few cable chain stitches with my new thread before I secured the old thread at the back. That way it's possible to change the look of the last stitch if necessary.
I hope this little trick is helpful for some of you.