Burn Bootloader steps

 

Step 1 : Connect Arduino UNO A to computer. 
Step 2: Load Examples > Arduino ISP to Arduino A.

Step 3: Connect between arduino A and arduino B

Arduino A to Arduino B

Pin 13 to Pin 13

Pin 12 to Pin 12

Pin 11 to Pin 11

Pin 10 to Pin Reset

Pin 5v to Pin 5v

Pin Gnd to Pin Gnd

Step 4: Connect computer to arduino A

Step 5: Select correct PORT and ARDUINO UNO

Step 6: Go to tools > Burn Bootloader.

Final step: Wait until note DONE UPLOADING