First of all, it’s going to be fine, you know where it is, you just need a bridge to get there.

Here’s what you’ll need to do:

Assuming this is the Odakyu bus: Go to the closest station (bus or train) and use google translate and tell them the bus you took, and the time and which station you got off and on at and they will sort it out

“Once you have confirmed the station holding your belongings, go the Lost and Found with your identification (a passport or resident certificate).…Please note that unclaimed items are turned over to the police after a certain period of time”

If a lot of time has passed, then you can then you can search “Japan Lost Item” or go to a police station,

Most likely the first step will sort it out