Processing knitted neck with a looping seam is one of the easiest ways, so even a beginner can cope with it. The essence of the tutorial is shown in the video, and below is a brief description of the work and the points that should be taken into account when performing this seam.

1. Knit the neck of the desired length and height (I have it about 3 cm). To determine the desired length, I usually measure with a centimetre tape along the inner (still virtual) edge of the neck (i.e. at a distance of 3 cm from the edge of the neck). I deduct approximately 1-1.5 cm below for the neck not to looked stretched. By the length, I determine the required number of loops for the strap. You already have a sample of the lower elastic band, so use it not to choose wrong length. To determine the length of the strap also consider elasticity of your yarn. If it is strongly stretched in an elastic band, then reduce length a little more. If it keep the elastic band well, you may leave it as it is and use your measurements.

2. Knit the last row of the strap (front row) with knit stitches (regardless of the pattern on your product) of a contrasting thread colour. With this row you make the elastic go as it should. It is more convenient to work with contrasting thread.

3. If you knit the bar on straight spokes, then sew it into a ring, if you knit on circular spokes, then immediately pin the bar to the neck. Usually I place the bar near shoulder seams, not on the back, so that there is no thickening at the junction of the strap and the neck. If you are a beginner, you can sew the bar to the neck.

4. Sew as shown in the video. This seam is elastic enough, but at the same time it keeps the neck and does not allow it to stretch.
Be prepared that you may not succeed for the first time — incorrectly calculated length of the bar, small or large. In one place it may be too stretched, and the other vice versa. Stitches, when performing the seam, fall off and go loose. This is OK, it may not work for the first time, but you will succeed the second time. For the third time it will seem a simple task, the main thing is not to give up and do not stop.

Good luck!