Homey off line and not accesable

Hi I have an old Homey (about 2018) and was working fine till this morning.
This morning my router was not working annymore and was mallfunctioning.
Now I have a spare router installed and internet is working again.
The wifi network however is changed to a Ubiquity Unify device instead with different SSID and password. The router has no wifi. I want to connect Homey to this new wifi network, but do not know how to do it.
When I try to connect to Homey via PC or IPAD or 4G telephone I get the message Homey is offline.
For some reason none of the flows is working anymore, because no lights are automatically switched on or off.
When I go to setup.athom.com on a windows 10 PC I get after selecting the language: download the app from apple store or google store, but I’m on windows 10 PC.
I turned Homey upside down for 15 seconds to go to recevory mode. Then Homey says go to setup.athom.com. On a iphone I went via Google Chrome to setup.athom.com and again is Homey offline?
Please help what am I doing wrong??

If I had something like that, I would try to transfer the old SSID and the old password to the new router. I think the 2.4GHz WLAN is also important for the Homey Pro. Also pay attention to the encryption WPA2-PSK etc.

Thanks Patsche!!!
After creating a new wireless network on the Ubiquity Unify with the same SSID and password as used before with Homey. Homey is now suddenly working again. Thanks a lot.