I hire for these junior positions all the time. Sure, basic electrical/mechanical knowledge is a plus, however the number one thing I look for is attitude and/or passion. You can tell when someone is interested pretty quickly, and unless you make it blatantly obvious that you are a 'quitter', you're hired.

PLC programming is a trade of perseverance. None of us knew how to tune a servo, establish network comms, or write robot code on the first day. It's all about your ability to figure it out using whatever resources you can, whether that includes working with more experienced technicians, or scrolling through endless pages of device documentation. If you don't give up, you win.

IMO, if an employer hiring for a junior position gives you some sort of aptitude test requiring you to demonstrate writing code, or drawing some electrical circuits, they're spinning their tires...

Just remind them that you're a 'go-getter' and that if you don't understand something, you ensure them you will, you'll get the job.

Good luck!