what would we do if one day aliens came to earth and said...

Assuming that violent resistance is not practicable, go for one of these:

The same way you try to deal with other landlords in life:

Ask about intergalactic "squatter's rights" law

Ask for a lease to be refinanced later at a higher interest rate

Offer to work as the "building superintendants." Failing that, as gardeners ( a la Adam & Eve.)

Try to vitiate their claim by marrying them! Once we've done that, it's community property and we have a RIGHT to it!

we would probably deploy some secret weapon we got an annihilate em, or maybe we have a doomsday weapon, destroy Earth or even solar system ie some sort of black hole.