Garden shredder does not stay on

I have a garden shredder al-ko h2200. The day i bought it, the guy who was selling it tested it on my eyes and everything went great. Next day i turn it on in my place and it doesn't stay on. There is this switch that is supposed to stay on but it doesn’t and i have to keep holding it to have it keep working which of course is undoable. I opened it and cleaned several times, there is not much to brake or change there, i have no idea what could be the issue.

Please help!