I do A/V installs and remote programming and I have carried a Pronto TS1000 for twelve years exactly for this purpose. Nothing is as good as creating Pronto codes than one of the first generation Pronto products! This includes Marantz up to the RC5200.

The challenge may be that you need an RS232 output. I use a Keyspan USB to RS232 adaptor as, years ago, several brands and models were available and that was consistently the one that always worked. Friends say that there are many more models available now but I have no brand or model information on that.

Barf is totally right, too. No matter what you know or don't know about the remote and the product, you really have to identify the brand and model, even if it's some brand like Geepas. That's a brand from India with a name that, I believe, when pronounced with an Indian accent, sounds like "cheap ass." I mean, what if one of us has actual experience with that unit and could save you weeks?