help needed fitting shower base on concrete slab

[built4thrashing]

im doing an extension to the family house and have hit a bit of a hurdle with how to fit a shower base on a concrete slab. The drain has been put in below the slab and comes up inside a recess/void in the concrete. This void is not accessible for outside the house as brickwork is already done.

any help apreciated .
willing to swap my trade (electrician/refrigeration) for someone to come fit it corectly.
Thanx