Install
Odin on your computer. Install the
SAMSUNG_USB_Driver_for_Mobile_Phones on your computer. Download the ROM for your model tab from
SamMobile Firmwares. (You;ll have to create a free account to download a file.) Extract the files from the download (extracting them to the same folder Odin is in makes things easier). Load the files into Odin - the names make it obvious which file goes into which slot.
Boot the tab to download mode. Connect it to the computer. You should see one of the boxes in the grid at the top of Odin turn yellow and show COM and a number (the number is unimportant). Start Odin. It should flash the ROM to the tab, then the tab should restart the way it was wen it was new.
(There are Odin tutorials with screen shots all over the web.)