Builder sold garden flat without garden in plan

In 2006 we purchased a ground floor flat with attached garden. The blueprints approved by corporation shows the garden part as open space and some scooter and bicycle parking. However on agreement, the open space is shown as garden in a diagram. Also, the garden area is mentioned in index 2 as well as agreement. We are in possession of the garden area. However the builder failed to revise the plan showing garden area as part of flat. Now I want to sell the flat. However, the purchasers bank is asking for revised plan for approval of loan. What can be done about this issue now?