kotlin, 173 bytes

Result

AC

Duration

5611ms

Code [DL]

fun main(){var s=readLine()!!
println(s)
val l=s.indexOf('T')
while(0<1){println(Regex("K.*r").replace(readLine()!!.replaceRange(l,l,"r"),{z->"r".repeat(z.value.length)}))}}

stdin

                    T                             
                                                  
       K                                          

stdout

                    T                             
                    r                              
       rrrrrrrrrrrrrr                              

stderr

OpenJDK 64-Bit Server VM warning: Options -Xverify:none and -noverify were deprecated in JDK 13 and will likely be removed in a future release.
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by com.intellij.openapi.util.JDOMUtil$2 to constructor com.sun.xml.internal.stream.XMLInputFactoryImpl()
WARNING: Please consider reporting this to the maintainers of com.intellij.openapi.util.JDOMUtil$2
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
Exception in thread "main" kotlin.KotlinNullPointerException
	at CodeKt.main(code.kt:4)
	at CodeKt.main(code.kt)

strace