You do not make 90 days reports if you just entered the Kingdom using a Non Immigrant O visa. But if you count your first 90 days it finish on the same day as your Admitted to Stay date as you get only 90 days to stay on entry.
So you are on the initial 90 days you got on entry, you can ask the Immigration Officer if you already have to make the 90 day report when you apply for the 60 days Extension of Stay based on family visit.
And with these wise words "Anyway, case happily closed and I know what to do now. Cheers π" I can close it for commenting.
Things do not keep on changing due to covid, Immigration made an extra service for those who are stranded, all the other Immigration rules and regulations did not change.
If you did not change, your old notification of address is still valid.
The letter support your old notification, I would say you can use both to show your address. No need to download an app, register the address and make a new registration.
Most Immigration Offices let you apply between 45 days before and the last day. I would say go now and get a re-entry permit once the new Extension is stamped in your passport.
If you come back on the 15th, 1 day hotel, you have a little time left to organize all.