I made a tiny wood mold and prepared a paper cup. I heated the flat acrylic piece with a heat gun, and placed it between the paper cup and wood mold. I wore a pair of thick gloves and forced the acrylic into that specific shape by hands.

The shape was fixed when the acrylic cooled down. Then I tore off the protective film and sanded the sharp edge.( The protective film should be torn in the final step! Otherwise it would be super easy to leave a burn mark on the surface which is extremely hard to remove.)