"I have System51 software
(DOS)and an Eprom where debug program in it "

Both the above have no independent existence and would have formed part of the total harwdare that you refer as "Target ". So where is that ?

And if I were you, I would contact the manufacturer somehow and proceed from there. If the manufacturer has closed shop, then throw both the above into the nearest bin based on your region's garbage displosal laws.

Raghu