I suspect that your actual problem isn't that you truly only want to know the internal resistance of the ammeter in question, but rather something else, and that you believe that knowing the internal resistance will tell you something about what you are actually trying to determine.

So what problem are you seeking to solve by asking this question?

I didnt go to university today and we had lab hours.In the laboratory we use a Protek IDM 505 and I didnt measure some circuits which are for homework so I am searching it online to see if I can find anything.

It sounds like you are saying that you didn't finish an assigned laboratory exercise, so you are looking for the appropriate values you can use to "fake it". If that's not the case and you really want to know then you need to find a proper datasheet for the meter.

Most of the resistance will be in the actual wires and probes, especially so for cheap instruments that come with low quality probes.