TBK 958a laser machine.. and the laser not work

Hello everyone please I need your help

I have TBK 958a laser machine.. and the laser not work .when I use the the laser machine it moving around thanks for ur help thank you

I know the laser machine are working but the problem is know the size of the laser.if I want remove back iPhone .for example I use for iPhone 8plus the laser get smaller so not remove all the back ..