Unable to connect Chamberlain garage door opener via 5g internet

I have spent much time and research with trying to connect to MY Q/chamberlain garage door opener wifi AP since changing both my phone and internet to T Mobile.   My recent contact with a Chamberlain support person has me certain that the problem lies with security settings within the Gateway router. Reading these posts and following recommendations from both My Q and T Mobile support  , it seems most likely that it is an issue with Port 8883 being blocked.   I am unclear how to "unblock" port 8883. 

I was told by T Mobile that the Gateway settings cannot be changed as it is preset and a plug and play device.  All of my connected wifi devices are working EXCEPT the My Q app.  

Any updates on how to remedy this ?  Thanks so much!