I've tried to replace camera lens on my own now zoom lens not focusing

First make sure that the lens is not dirty to any degree, it’s extremely easy to dirty the lens on install however if that’s not the case it’s also worth checking the camera and lens for any hairline cracks. I’ve installed several new lens’s and checked for cracks prior and then after being dumbfounded for a few mins I’d take it under the microscope and find the smallest crack on the camera causing focusing issues; it’s extremely common especially when replacing only a lens after a break because it’s very easy for the camera to also sustain minor damage and honestly I’d say it’s pretty rare for it to not.