Hi
It is not possible to directly restore a deleted watch face that has been customised with complications.
However, you can easily add a new watch face and then repeat any customisation:
When viewing the time on your watch: firmly on the watch face, swipe left until you reach the New watch face option > tap on the New button "+" > scroll to your preferred watch face (using the Digital Crown) > tap on it to select it.
To customise the watch face complications:
To make complications available for installed apps:
On your iPhone, in the Watch app, go to: My Watch (tab) > Complications > tap Edit (upper-right).
Keep in mind that some apps may not support all locations / sizes of complications on any given watch face.