Smart Thermostat for location with only MiFi Router access

I want to use a Smart Thermostat for an association building that does not have an Internet connection.
For the Internet connection I am thinking of a MIFI Router with a 4G pre-paid card.
I am now able to access Internet from within the building.
But can I now also remotely connect to the Smart Thermostat to adjust his settings and program?

Does anyone have a solution for a situation like this?

Kind regards, Bert
Ps. There is no HA available in the building; but that would be an alternative.

Set up a VPN

Thank you @nickrout for your reaction.
I understand the use of a VPN, I use it for my HA at home as well. But in this case the VPN can only be initiated at the MiFi router OR at the Honeywell Lyric T6 thermostate.
I have a Huawei E5577 at my disposal which i would like to use. And if it is possible to create a VPN with such a device, I wonder what the data consumption will be, using a 4G connection. I guess there will be lots of keeping alive packages floating back-and-forth…

I found this article: Can you use a VPN with Huawei e5577
and will try to experiment with it: