How to fix after dumb update attempt

I was looking at my Nextcloud install, and saw a file with these instructions:

#!/usr/bin/env bash
docker-compose pull
docker-compose up -d

That looked really easy, so I thought I’d try it. Now the database is starting OK, but Nextcloud is not. When I run docker-compose up I get:

app_1  | Initializing nextcloud ...                                                                                            
app_1  | Can't start Nextcloud because upgrading from to is not supported.                                            
app_1  | It is only possible to upgrade one major version at a time. For example, if you want to upgrade from version 14 to 16, you will have to upgrade from version 14 to 15, then from 15 to 16.

What would be the best way to get up & running again?