i want erase ipad with broken screen and find my ipad is shut off

i cracked my screen on my ipad pro 11", it was still working, I wanted to send it back to Brightstar who I have a warranty with. when i called them about service I had to shut off the find my phone/ipad feature.

the next day i tried to turn it on and only a black screen but working'

i need to erase the content before i can send it back

HELP!

thanks in advance