Which support page suggests you do a factory reset?
I should’ve screen shot it, my app suggested it.
Can’t say I’ve ever seen that in the Sonos App (…or mentioned elsewhere🤔?) Anyhow, if the device is your one and only Sonos product and its status LED is flashing green, post-reset, you will also need to reset your Sonos App (or remove/reinstall it, if you prefer) and follow the steps for a "new system’ setup.
Do not choose an ‘existing’ system setup, because you no longer have one, that’s if you are sure you have factory reset your one and only product.
If things still do not work for you after trying those steps, then perhaps try temporarily wiring the device to the local router to help to get it setup on your new network, but you will then need to go through some further steps afterwards to switch the speaker over from ‘wired’ to ‘wireless’ mode, as explained in this Sonos Support Link:
https://support.sonos.com/en-us/article/switch-sonos-between-a-wireless-and-wired-setup