How do I fix a detached screen on an iPad after accidentally bending it?

If the iPad chassis has been sufficiently deformed to detach the screen, it will require repair. If the screen has been displaced, there may be additional damage to other internal components, such as the iPad's battery - this, of itself, representing a possible safety consideration.

That said, given a bent casing represents significant physical damage, Apple may decline to offer repair for your iPad. Be aware that physical and consequential damage are non-warranty.

For practical purposes, in lieu of repairing and returning your own iPad, Apple usually exchange a qualifying iPad for a renewed/refurbished iPad of the same model and specification. The cost of the exchange is the same as would otherwise be charged for repair. Unless you have benefit of an active AppleCare plan, an out-of-warranty repair will likely be expensive.

As for out-of-warranty repair costs, Apple offers a fixed-price price repair. You can verify eligibility and cost for your region/country here:

iPad Repair & Service - Apple Support

If you have an active AppleCare+ plan, the cost of repair is reduced to a small excess/deductible fee.