I am using and AT&T simcard getting excellent 4G/LTE speeds and needed a Static/Public IP.
I have ordered it from my wholesaler/vendor who I get my service activation from and they told me the IP address and APN to enter...
I have entered the APN but I do not know where to put the the Static/Public IP.
I also have this same issue/request for a T-Mobile sim card that I have received the new APN and Static public IP address, again, I do not know where to enter the IP.
Any assistance would be appreciated.
Bob.

Something you could try:
[admin@MikroTik] > ip address add address=<your public ip> interface=<your lte interface>

I do not know if this would be the correct way but it is the only place that makes sense to me.

You could also contact your vendor and ask them.

I'm pretty sure you don't have to enter IP address anywhere, you should be getting it as you'd get the dynamic one.