Guys please help me, I underwatered my Airplant and it got all brown in the bottom how can I save it
Damage from underwatering starts from leaf tips. This damage of plant base is probably rot caused by incorrect watering (overwatering). I think at this point your plant is already dead. You can confirm that by removing visibly dead leaves and smelling the plant base. If you can smell rot, it's over. Only tillandsias with prolonged stem can be sometimes saved by cutting away the bad part.
Here's a closer look. I really love this air plant and I'll be so sad if it dies
Yes, this looks like seriously bad rot. Tillandsias should get dry fast enough after watering. In 3-4 hours recommended. During winter don't pour water inside the plant center where it can't evaporate fast enough. Just turn it upside down and mist it whole about 2-3 times per week. After that put it at warm dry place.
Well it's really dead because I took a look at the pup and it just fell apart but the good news is that my other air plant is doing really well and is even starting to flower