my iPhone 8 touch key is damaged

I suggest that you make an appointment (*) and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple – Location Selector. After checking it out, they'll give you all the available options.

Regards

Giulio

(*) You can do it:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above;
• Using the "Apple Store" app, available and downloadable from AppStore.

Seeing the image you posted (screen seriously damaged) I think you'll need a full new screen (but Apple technicians will judge after evaluating).

Should be this case, get an estimate here:--> iPhone Service & Repair - Apple Support

(prices valid in US Apple Stores, tax excluded, work included).

Regards

Giulio