Welcome to the site
The problem is it is there to stop people changing things, so the person who set it is the one to ask.
On some equipment passwords can be re set by main agents others on others not.
We use equipment that only the manufacturer can re set after it is set & lost , stops a lot of theft.
Simple but obscure is the way to go, hope you find the one who set it
Thank you very much for the answer.
The welding machine is second hand.
I will ask for the password from the seller.
Otherwise, it worked without any problems for 14 months.