#Java 8, 159 158 bytes

n->s->{for(int i=s.length,j;i-->0;)for(String x:"1234567890;QWERTYUIOP;ASDFGHJKL;ZXCVBNM".split(";"))if((j=x.indexOf(s[i])+n)>=n)s[i]=x.charAt(j%x.length());} 

-1 byte thanks to @OlivierGrégoire modifying the input-array instead of printing directly.

Explanation:

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n->s->{ // Method with integer and character-array parameters, and no return-type for(int i=s.length,j;i-->0;) // Loop over the input character-array with index for(String x:"1234567890;QWERTYUIOP;ASDFGHJKL;ZXCVBNM".split(";")) // Inner loop over the qwerty-lines if((j=x.indexOf(s[i])+n)>=n) // If the current qwerty-line contains the character // Set `j` to the index of this character on that line + input `n` s[i]=x.charAt(j%x.length());} // Replace the character at index `i` // with the new character (at index `j` modulo length_of_qwerty_line) 

Java 8, 159 158 bytes

n->s->{for(int i=s.length,j;i-->0;)for(String x:"1234567890;QWERTYUIOP;ASDFGHJKL;ZXCVBNM".split(";"))if((j=x.indexOf(s[i])+n)>=n)s[i]=x.charAt(j%x.length());} 

-1 byte thanks to @OlivierGrégoire modifying the input-array instead of printing directly.

Explanation:

Try it online.

n->s->{ // Method with integer and character-array parameters, and no return-type for(int i=s.length,j;i-->0;) // Loop over the input character-array with index for(String x:"1234567890;QWERTYUIOP;ASDFGHJKL;ZXCVBNM".split(";")) // Inner loop over the qwerty-lines if((j=x.indexOf(s[i])+n)>=n) // If the current qwerty-line contains the character // Set `j` to the index of this character on that line + input `n` s[i]=x.charAt(j%x.length());} // Replace the character at index `i` // with the new character (at index `j` modulo length_of_qwerty_line) 

#Java 8, 159 bytes

n->s->{int i;for(char c:s)for(String x:"1234567890;QWERTYUIOP;ASDFGHJKL;ZXCVBNM".split(";"))if((i=x.indexOf(c)+n)>=n)System.out.print(x.charAt(i%x.length()));} 

Explanation:

Try it online.

n->s->{  // Method with integer and character-array parameters, and no return-type int i;  // Index-integer  for(char c:s) // Loop over the input character-array for(String x:"1234567890;QWERTYUIOP;ASDFGHJKL;ZXCVBNM".split(";"))   // Inner loop over the qwerty-lines if((i=x.indexOf(c)+n)>=n)   // If the current qwerty-line contains the character   // Set `i` to the index of this character on that line + input `n` System.out.print(x.charAt(i%x.length()));} //  And print the character at index `i` modulo length_of_qwerty_line 

#Java 8, 159 158 bytes

n->s->{for(int i=s.length,j;i-->0;)for(String x:"1234567890;QWERTYUIOP;ASDFGHJKL;ZXCVBNM".split(";"))if((j=x.indexOf(s[i])+n)>=n)s[i]=x.charAt(j%x.length());} 

-1 byte thanks to @OlivierGrégoire modifying the input-array instead of printing directly.

Explanation:

Try it online.

n->s->{ // Method with integer and character-array parameters, and no return-type for(int i=s.length,j;i-->0;)  // Loop over the input character-array with index for(String x:"1234567890;QWERTYUIOP;ASDFGHJKL;ZXCVBNM".split(";")) // Inner loop over the qwerty-lines if((j=x.indexOf(s[i])+n)>=n) // If the current qwerty-line contains the character // Set `j` to the index of this character on that line + input `n` s[i]=x.charAt(j%x.length());}   // Replace the character at index `i` // with the new character (at index `j` modulo length_of_qwerty_line)