As I understand it, you are asking how to discover what virtaul address corresponds to a particular physical address. The answer is that there is not necessarily any such address, or there may be several.
I presume the reason that you need this is so that you can alter page tables, and other structures that must use physical addresses. The answer is that you have to set up your own mapping to do this. A simple solution is to map all physical memory to a particular range of virtual addresses - this only really makes sense in a 64-bit environment where you have a practically unlimited address space. Another answer is to use recursive page tables (
https://wiki.osdev.org/Page_Tables#Recursive_mapping ), although it can be a bit difficult getting your head around this. Or you can reserve a small range of virtual addresses and map individual pages as needed - but this is relatively inefficient. I use the first method - it does use up some available memory, but probably not as much as you might imagine, particularly if you are not working with a huge amount of RAM. If you do this you have to ensure that this mapping is only available to the kernel, not to user programs.