No dumbbells, no problem. Press it out anywhere.
Keep your ribs down and core braced so you don't arch your back as the band fights you.
Anchoring the band under your hips and pressing overhead loads the delts against tension that climbs all the way to lockout, where the triceps finish the job against the band's hardest pull. Sitting removes the leg drive and torso sway that standing presses invite, so the shoulders can't outsource the work. It's a genuinely useful overhead press for home training, and the top-heavy resistance builds exactly the lockout strength that free-weight pressing tends to leave soft.
That's the band's strength curve, maximum stretch at lockout means maximum tension right where your arms straighten. It feels backwards compared to free weights, but that's the value, it forces you to finish reps rather than bailing near the top.
Brace before the press, ribs down and abs on, and sit tall rather than leaning back to turn it into an incline press. If the arch creeps in anyway, reduce the band tension, an arched press is just a worse exercise.
Straight overhead, finishing with your biceps roughly beside your ears. Behind-the-neck pressing demands shoulder mobility most people don't have, and pressing too far forward turns it into a front raise.
