Hello,
How would I be able to get the Roco 63050 to work on Marklin C-tracks. I understand I might need a new decoder but which decoder would this be and how would I be able to make it work?

Thanks

I don't know this model, but with Roco and some other brands, there are issues that need to be addressed.

1) Most of the models have one powered unit and the rest are non powered.
2) You will need one or two sliders to pick up power from the center rail.
3) If you want to have power selection from the leading end of the train, you will also need to either install a relay or procure a decoder which has an integrated relay.
4) There are often differences between the 2 rail DC and 3 rail AC units which involve how many wheels are motor driven and how many are used for current collection. There are also often differences in the underside of the bogie parts, to allow for the installation of the AC slider.
This model has 4 powered wheelsets, including 2 wheelsets with traction tires.

The parts list (Page 2) shows 6 parts that you will need to source for an AC conversion.
From what I can see, you do not need to replace bogie parts for a conversion:
https://www.roco.cc/doc/et/1/de/63052_10165.pdf

Regards

Mike C