How to get custom value in datagridview windform C#

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C#4.0

C#3.5

C#6.0

I have one table in sql

<br />
Sl | Grade | Remark  <br />
1  | A     | ggggggggggggggggggg<br />
2  | B     | ddddddddddddddddddd<br />
3  | C     | dddddddddxxxxxxxxxx<br />
4  | D     | rrrrrrvvvvvvvvvvvvv<br />

Now my question is to retrieve grade from sql table by filling Sl in datagridview1 textbox.

if I fill 2 in datagridview textbox column (SL)
SL | Grade | Remark
2 | |

then It should retrieve its grade from sqltable

<br />
Sl | Grade | Remark  <br />
2  | B     | ddddddddddddddddddd<br />

What I have tried:

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