for example there is string "hello world\0" in usermode program at virtual address 0x0000f000 how to edit that string from driver ?
i know that chars can be noncontinuous if we look from physical memory but i dont care how to edit at least first char ? or how to edit integer for example ?
how to convert virtual address to physical ?
thanks in advance.

> know that chars can be noncontinuous if we look from physical memory

Minimal page size is 4 KiB so your 12 Byte's at VA $0000'F000 (???) will be continuous.

> how to convert virtual address to physical ?

Find out what value (physical address) the victim app has in CR3. Please send me your virus when it's done (encrypt it well otherwise I won't be able to get it).

The best way is always to use another app/dll that talks (IO) to the driver.