Chosen Solution
I recently toon my screen off. When reattaching it, the display have horizontal lines going through the whole screen. What would needs to be replace in this case?
Ouch! You managed to damage the display. The cost of a new display is about $85 ~ 120 depending on the size and glass. Apple just lowered the price of the Series 3 depending on how worn yours is you might consider it.
If you struggle to find a new screen look on eBay for a spares or repair watch the same as yours with a good screen and use that. Cheaper than a new one too. I used to repair fitbits this way.
This is what it looks like, so I’m not sure if I messed up the display or the connectors. Update (10/05/2022) When powering on it looks like this
