pi 4 – Scheduling a task with cron

I have digital signage software on raspberry Pi 4. It needs restarting 3 times a day to update menus. I have been looking into Cron jobs for this. I don’t have any experience with Linux terminals and I have fallen at the first hurdle. After struggling to navigate the terminal, I have tried launch the program (posterbooking)to see if I have the correct path before attempting to configure a cron job. So far, I have typed in this path – cd usr/share/applications/posterbooking.desktop

which I got from here –

It would not boot. My eventual plan was to schedule the raspberry pi to restart 3 times a day with posterbooking starting automatically on startup. Any advise on this will be very appreciated.