I found an iPhone SE that was locked because it was lost. I would like to reset it so I can use it.

Without the original owner’s assistance, the iPhone will remain useless forever. It is Activation Locked - an anti-theft mechanism.

How to remove Activation Lock - Apple Support

Turn it over to the authorities.

Just in case it wasn't clear, with this iPhone being Activation Locked, there is nothing anyone here, nor Apple can do to assist you with getting it unlocked. Only the original owner can do so ... and if they lost it, I'm sure they would like to get it back. Just finding it doesn't make you the new owner.

Turn it over to the police or a lost and found where you found it. Without the passcode and activation lock information, that phone is useless to you.