How do I remove activation lock from my Apple device?

Ss885 wrote:

I bought this product second hand and have the bill.

Activation Lock is a theft deterrent, a d is intentionally difficult to bypass.

We can’t help, and absent convincing proof of ownership — an original receipt from Apple or an Apple authorized reseller — Apple won’t help.

Which means it is a brick. Return it to the seller. Either they unlock it, or they refund your purchase, or (as happens all too often) they’ve absconded and that’s why you’re asking here. If the seller has absconded, recycle it.