ZTE MF286D - QMI How to Force 3G or 4G?

I have OpenWRT with QMI working but cannot see how to set / force 4G only or 3G only. 3G is a much faster & stronger service where I'm living so I'd like to set that. At the moment, the router switches between 3G & 4G at random intervals.
Is there a menu that has the capability to set 3G or 4G , or perhaps a CLI command?

Thanks

config interface 'wan'
        option proto 'qmi'
        ...
        option modes 'umts'
        ...
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Thanks for the pointer, I tried -option modes 'lte'- in /etc/config/network and the router booted into LTE but I was not able to access the internet, removing the line booted back to 3G and all working again. I tried lte as it is not the mode that the router normally starts but does switch to from time to time.