I know the fourth rep was weak, but should I increase the weight next workout or reduce it and work on my form? Sorry for the rotated video
Add weight. Your form looks decent; I’m sure there are details that could be improved (such as pushing with your hips and staying more vertical on the way up), but as long as your reps look acceptable, it is important to add load. People keep practising with light weights and never understand that you need to reach your breaking point to find the relevant flaws in your form. You controlled the weight for five reps even though you lost confidence during the fourth; this means you can add weight. When you fail to get five reps on your last set (not five ‘perfect’ reps), deload to 90%.