You have 2 options:

1. Test the card quickly without reinstalling the fan/heatsink.

Do not operate the GPU with heatsink/fan removed for more than 30 seconds.

2. Reinstall the fan/heatsink, then test the card.

Repeat steps 2-9 if GPU fails test.

Proceed to step 10 if GPU passes test.

Most people will want to test the card to see if it powers on and passes the POST.