Where to begin ?
Expenses are costs, presumably what you mean is that your employer gave you money to pay for hotel/train/ meals. So you received the money and paid the cost. In general these things pass through, (income-cost= zero) and so no tax is payable.
However there are some restrictions on what costs are allowed in these circumstances.
You seem to have paid tax on the money you received already, how ? Via PAYE?
Whatever mechanism taxed you should recognise the cost and reduce your tax by the allowable amount.
The form 11 due in by Tuesday is for 2016.
You would need to provide more detail to get a more detailed reply.