Employment income is entered in box 1 on the Employment pages. Don't enter any foreign tax in box 2.
How you enter foreign tax depends on whether or not you want to claim tax credit relief.
Go to Your work > Work abroad
Enter the total in the box Any foreign tax paid for which you are not claiming foreign tax credit relief.
Go to Additional Information > Page 2
Complete the information in box 13 for Foreign tax for which tax credit relief not claimed.