Warmme app and Heat/it thermostat

First post, just joined today so pls be gentle…
My Heat/It [ ET-84W] Thermostat box had the blinking wifi … no longer… and i can’t get it back to connect the Warmme app to it. I tried total reset without success. Help?
Also, am i correct in thinking this box and app dont work with 5G internet?
Apologies for the low level of knowledge… I am getting on in age…