Declaring completion of works (swimming pool)

I have received a letter from the 'Service des Impots Particuliers, Secteur Foncier’
We have to declare the completion of the work on our swimming pool. The letter states that I must print form H1 from the Impots.gouv website to complete and send to them.
I have done this but can see nowhere on there that mentions ‘Piscine’ I can only see where to put our name and address and date of work completion, everything else refers to house building, extensions etc.

I called into our local tax office and they were as clueless as i am !!!
I’m sure some of you have already done this, can anyone advise me please ?