I have a requirement to match column 4 (Grade) from File1 csv with column 1(Grade) of File2 , if matches then replace column 4(Grade) of File1 csv with Column2 (Marks) of File2. if not matches then leave previous value of column 4 (Grade) as is.

File1

"RollNo","Name","Age","Grade","Class","Teacher"

"1","Asha","7","A","1","David"

"2","Mona","7","B","1","David"

"3","Sonali","7","C","1","David"

"4","Rani","7","D","1","David"

"5","Raj","7","B","1","David"

File2

"Grade","Marks"

"A","90"

"B","80"

"C","70"

Expected Output:

"RollNo","Name","Age","Grade","Class","Teacher"

"1","Asha","7","90","1","David"

"2","Mona","7","80","1","David"

"3","Sonali","7","70","1","David"

"4","Rani","7","D","1","David"

"5","Raj","7","80","1","David"

Can you please help me with how awk command should be for this Output ? Looking ahead for your response

I have a requirement to match column 4 (Grade) from File1 with column 1  (Grade) of File2. If it matches, replace column 4  (Grade) of File1 with column2 (Marks) of File2. If it doesn't match, then leave the value of column 4 (Grade) as is.

File1

"RollNo","Name","Age","Grade","Class","Teacher" "1","Asha","7","A","1","David" "2","Mona","7","B","1","David" "3","Sonali","7","C","1","David" "4","Rani","7","D","1","David" "5","Raj","7","B","1","David" 

File2

"Grade","Marks" "A","90" "B","80" "C","70" 

Expected output:

"RollNo","Name","Age","Grade","Class","Teacher" "1","Asha","7","90","1","David" "2","Mona","7","80","1","David" "3","Sonali","7","70","1","David" "4","Rani","7","D","1","David" "5","Raj","7","80","1","David" 

Can you please help me with an awk command for this output? 
Looking ahead for your response.