Depends on how it’s been 1st fixed. I always put 15mm copper out of the wall and use a shower bar fixing kit, the 3/4 unions on the shower bar then screw straight to those using a fibre and rubber washer between. That way (any) leaks are shower side not in the wall.
If you’ve got 3/4 female irons in the wall already (and aren’t removing tiles), the Hansgrohe bar comes with cranked male to male fittings to screw into those, and a shroud to cover the threads but they can be a PITA to get level and also there’s a point of leak in the wall where you can’t see it, so I always bin them and use my top method if new install, the latter I’d only use for retrofit.
having said all that, HG use 150mm pipe centres, so if your existing does, you might be able to easily just replace the bar