How to clear data readed by scanner from textbox to recieve

Problem

When read qr using barcode scanner for more than one it append the same textbox4 .

i need to clear data after every scanning done .

Details

I using usb scanner reader qr code with type metro logic working as keyboard

and using USB

i read data in textbox4 key down success

but problem if i read data for new qr code

it append in same text box

so that what i do to clear the data recieved before and prevent append to old

my code

textbox4 read data from reader device then split them to textboxes