Shimano 105 right crank compatibility question
 

I am a cycling beginner and I have a Triban rc520 outfitted by a FC-RS510 - Shimano crankset, unfortunately the right crank had a lose thread. The only available replacement parts in my country is a Shimano 105 r7000. My question is can I use a Shimano 105 r7000 right crank as a replacement for the FC-RS510? or do I have to replace the whole crankset? Any other suggestions are appreciated. Thanks.

What thread is loose?
As the right crank includes the axle as a one piece unit can't see what loose thread could be a problem.

And if this is a new bicycle, then definitely take it back to them as see what they say. Then see if they'll let you watch as they solve the issue. Then you'll know more for the next time something similar happens.

You're going to have to clarify what you mean.

As mentioned, the drive-side (right) is a one-piece assembly with the spider, spindle and crankarm. I assume that you're not talking about the chainring bolts... are you talking about the captive threading for the pedal spindle? If that's what you're talking about, yeah - you're going to need the whole drive-side assembly and you might as well replace the whole thing, if it's not in warranty.

The right crank comprises the crank arm along with the chainrings and spindle, about 80% of the whole crankset. If you could find just that part, it would cost about as much as the full 105 crankset. Perhaps you could furnish a bit more information about the damaged threads on your crank