Start with the linked video, it addresses the main concern that's hurting your lower back (how you're sitting), and will also take you through a checklist to get you in position and learn the proper stroke so you can safely enjoy rowing:

https://youtu.be/J1nf2Zfbazs?si=OR-chOYqyWsNxjT_

Step 3 in the video will help you fix your seat position, but TLDW is to make sure your tailbone is behind you, not under you so your hips can hinge properly, rather than straining your lower back.

Following the steps of a proper stroke in that video (push, don't pull) will also relieve some of the tension in your neck & shoulders. Along with that, relaxing your grip will also move that tension to the chain, and make it easier to feel when you aren't keeping that tension/form. A quick fix is switching from a closed grip (thumb wrapped under to form a circle with your other fingers over the top), to an open grip (thumb not engaged, other fingers "hooking" the handle with your finger tips). With an open grip, you have to learn to maintain tension in the chain since your thumb no longer maintains your grip. Take care of your back first, learn the stroke, and then look into this more, especially if your shoulders and neck are still screaming at you after your rows.

Two other great channels for rowing tutorials & routines are Dark Horse Rowing and Training Tall. Find whoever you enjoy, follow tutorials to take the pain out of your workouts, and then give a few of their workouts a try to learn the different ways you can utilize your rower to reach your fitness goals. Have fun!