Your tension dial is missing. What you have is often referred to as a Singer 15 "clone." There are lots of pics on this thread:
Will the Real 15 clone please stand up that will show you how your machine should look. I don't know how different the tensions are on different makes of machines, but I would think you should be able to find what you need fairly easily. Someone more knowledgeable will be along shortly with more help.
ETA I just did a quick ebay search and found several tension assemblies for a model 15. Here is one:
https://www.ebay.com/itm/Vintage-Sin...4AAOSwK2JckPln
I also just noticed you seem to be missing an inspection plate, unless you have removed it before taking pics.