you should only need to change the wifi password if you have changed your wifi password, or you could get a wifi repeater to improve your signal strength, and if that was on a different SSID then yes, would need to change the password
that is you connecting to the admin console on the dongle. It has a web browser on it. The username/password is usually admin/admin and if you can login then you can change the wifi password/SSID that the dongles are trying to connect to.
If the login password is something different then you are going to have to factory reset the dongles to be able to change the wifi they connect to. There’s a reset button I believe on the back, its not something I have ever had to do though
LAN connection much simpler if you have LAN cables to your AIO and gateway
Once you login, you are logged in to the dongle, not the inverter itself. All you can do is change the wifi details and hotspot that the dongle provides. Some installers leave the hotspot unsecured so check that it has a password set.
So this isn’t going to give you a route to controlling/querying your inverter, sorry
The option most people use is the givenergy app which communicates to the givenergy portal and in turn back to your AIO. This all needs a decent network connection to your AIO though so you need to get this sorted out.
Alternatively there are a couple of local control options, the BBC Basic inverter app (iOS and Android) or the Android inverter app.
Next option is to install Home Assistant which will give you local inverter control via GivTCP. HA runs on a Raspberry Pi, NUC, PC or similar. A whole load of options for control with write your own scripts to control GivTCP or things like Predbat that do it for you.
Finally there are cloud based services that will control your inverter. Wonderwatt, My Energy Optimiser and Predbat.com, all are cloud subscription services. All communicate to your inverter via the givenergy portal so need that inverter to portal link working well first
All depends how hands on you want to be and where you want to go with the journey.